diff --git a/zipline/gens/mongods.py b/zipline/gens/mongods.py
index 417a1f70..303fd465 100644
--- a/zipline/gens/mongods.py
+++ b/zipline/gens/mongods.py
@@ -4,18 +4,20 @@ Generator-style DataSource that loads from MongoDB.
 
 import pytz
 import logbook
+import pymongo
 
 from pymongo import ASCENDING
+from datetime import datetime, timedelta
 
 from zipline import ndict
-from zipline.gens.utils import stringify_args
+from zipline.gens.utils import stringify_args, assert_datasource_protocol
 
 import zipline.protocol as zp
 
-def create_pymongo_iterator(self, collection, filter, start_date, end_date):
+def create_pymongo_iterator(collection, filter, start_date, end_date):
     """
     See the comments on :py:class:`zipline.messaging.DataSource` for
-    expected content of self.filter. Spec must adhere to that definition.
+    expected content of filter. Spec must adhere to that definition.
     Returns an iterator that spits out raw objects loaded from MongoDB.
     """
     log = logbook.Logger("MongoDBQuery")
@@ -28,12 +30,12 @@ def create_pymongo_iterator(self, collection, filter, start_date, end_date):
 
         # Add the list of sids that we care about.
         if name == 'sid':
-            assert isinstance(value, sid)
+            assert isinstance(value, list)
             sid_range = {'sid':{'$in':value}}
             spec.update(sid_range)
             
     # limit the data to the date range [start, end], inclusive
-    date_range = {'dt':{'$gte':self.start, '$lte':self.end}}
+    date_range = {'dt':{'$gte': start_date, '$lte': end_date}}
     spec.update(date_range)
 
     fields = ['sid','price','volume','dt']
@@ -41,8 +43,8 @@ def create_pymongo_iterator(self, collection, filter, start_date, end_date):
     # In our collection, load all objects matching spec.  Of those
     # objects, get only the fields matching fields, and return the
     # loaded objects sorted by dt from least to greatest.
-
-    cursor = self.collection.find(
+    
+    cursor = collection.find(
         fields   = fields,
         spec     = spec,
         sort     = [("dt",ASCENDING)],
@@ -53,17 +55,46 @@ def create_pymongo_iterator(self, collection, filter, start_date, end_date):
     cursor = cursor.hint([('dt', ASCENDING),('sid', ASCENDING)])
 
     # Set up the iterator
-    iterator = iter(self.cursor)
+    iterator = iter(cursor)
     log.info("MongoDataSource iterator ready")
+    
     return iterator
 
 
 def MongoTradeHistoryGen(collection, filter, start_date, end_date):
+    """A generator that takes a pymongo Collection object, a list of
+    filters, a start date and an end_date and yields ndicts containing
+    the results of a query to its collection with the given filter,
+    start, and end.  The output is also packaged with a unique
+    source_id string for downstream sorting
+    """
     
+    assert isinstance(collection, pymongo.collection.Collection)
+    assert isinstance(filter, dict)
+    assert isinstance(start_date, (datetime))
+    assert isinstance(end_date, (datetime))
+    
+    # Set up internal iterator.  This outputs raw dictionaries.
     iterator = create_pymongo_iterator(collection, filter, start_date, end_date)
-    source_id = "MongoTradeHistoryGen" + stringify_args(collection, filter, start_date, end_date)
 
+    # Create unique identifier string that can be used to break
+    # sorting ties deterministically
+    argstring = stringify_args(collection, filter, start_date, end_date)
+    source_id = "MongoTradeHistoryGen" + argstring
+
+    # All datasources
     for event in iterator:
+        # Construct a new event that fulfills the datasource protocol.
+        event['type'] = zp.DATASOURCE_TYPE.TRADE
+        
+        event['dt'] = event['dt'].replace(tzinfo=pytz.utc)
+        event['source_id'] = source_id
+        payload = ndict(event)
+        assert_datasource_protocol(payload)
+        yield payload
+
+    
+        
         
     
             
diff --git a/zipline/gens/utils.py b/zipline/gens/utils.py
index 0c2f468d..27454fb7 100644
--- a/zipline/gens/utils.py
+++ b/zipline/gens/utils.py
@@ -1,5 +1,40 @@
+import pytz
+import numbers
+
+from hashlib import md5
+from datetime import datetime
+
+from zipline import ndict
+from zipline.protocol import DATASOURCE_TYPE
+
+
 def stringify_args(*args, **kwargs):
-    """Define a unique string for any set of args."""
+    """Define a unique string for any set of representable args."""
     arg_string = '_'.join([str(arg) for arg in args])
-    kwarg_string = '_'.join([str(key) + '=' + str(value) for key, value in kwargs])
+    kwarg_string = '_'.join([str(key) + '=' + str(value) for key, value in kwargs.iteritems()])
     combined = ':'.join([arg_string, kwarg_string])
+    
+    hasher = md5()
+    hasher.update(combined)
+    return hasher.hexdigest()
+    
+
+def assert_datasource_protocol(event):
+    """Assert that an event meets the protocol for datasource outputs."""
+
+    assert isinstance(event, ndict)
+    assert isinstance(event.source_id, basestring)
+    assert isinstance(event.dt, datetime)
+    assert event.dt.tzinfo == pytz.utc
+    assert event.type in DATASOURCE_TYPE
+
+def assert_trade_protocol(event):
+    """Assert that an event meets the protocol for datasource TRADE outputs."""
+    assert_datasource_protocol(event)
+
+    assert isinstance(event, ndict)
+    assert event.type == DATASOURCE_TYPE.TRADE
+    assert isinstance(event.sid, int)
+    assert isinstance(event.price, numbers.Real)
+    assert isinstance(event.volume, numbers.Integral)
+    
diff --git a/zipline/protocol.py b/zipline/protocol.py
index 4822b658..98245981 100644
--- a/zipline/protocol.py
+++ b/zipline/protocol.py
@@ -231,7 +231,6 @@ def DATASOURCE_FRAME(event):
 
     - *payload* a msgpack string carrying the payload for the frame
     """
-
     assert isinstance(event.source_id, basestring)
     assert isinstance(event.type, int), 'Unexpected type %s' % (event.type)