24 



which they are referred. Even here, however, there is a difference, H. sub- 

 pulchella having more diaphragms in the axial region than H. subpulchella 

 parvulipora. 



Locality. — Credit river, Streetsville. 



No. 12161, Royal Ontario Museum of Paleontology. 



HOMOTRYPA CREDITENSIS, Sp. tlOV. 



Plate III, Figures 3 and 4; Plate VII, Figure 5 



This member of the Homotrypa communis group of Bryozoa occurs in the 

 zone of Homotrypa streetsvillensis, in association with the type species of the 

 zone. H. creditensis is the only member of the genus in the Credit River section 

 which bears monticules. These are distributed regularly over the surface of 

 the zoarium with an average distance of three millimetres between them. Their 

 character cannot be determined by an examination of the surface, but tangential 

 sections show them to be composed of mesopores, surrounded by zooecial tubes 

 of almost twice the average size. 



In tangential sections, the zooecial tubes are seen to be small, twelve occurring 

 in two millimetres. Their walls are thin for the greater part of their course 

 but appear thicker near the surface of the zoarium, as the mesopores in this 

 part are filled with a secondary deposit of calcite. Numerous angular mesopores 

 are scattered throughout the zoarium as well as being grouped into the monticules 

 as mentioned above. Acanthopores are present but are small and unimportant. 



In vertical sections, it is seen that cystiphragms only are present in the 

 zooecial tubes. They are restricted to the younger part of the mature region, 

 both zooecia and mesopores being empty near the surface. Closely crowded 

 diaphragms are found in the mesopores. 



H. creditensis is closer to H. nodulosa, Bassler, than to any other form, 

 these two species being very similar in vertical sections, but differing decidedly 

 in tangential sections, and in growth. 



Locality. — Credit river, Streetsville. 



No. 12162, Royal Ontario Museum of Paleontology. 



Homotrypa streetsvillensis, sp. nov. 

 Plate III, Figures 5 and 6; Plate VI, Figure 5a, b, c; Plate VII, Figure 4 



A ramose representative of the Homotrypa communis group is found in 

 such numbers in a definite horizon of the Streetsville member that it has been 

 selected as the type fossil of the zone. 



In this species the branches vary from five to ten millimetres in diameter, 

 and in some cases reach a length of 50 mm. The surface is smooth without any 

 indication of maculae; the apertures indicate thick-walled zooecia of small 

 but uniform size — twelve in two millimetres. 



In tangential sections, the mesopores are few in number and the tubes 

 polygonal in shape, but as the axial region is approached the mesopores become 

 numerous and the tubes become rounded or oval in shape. Acanthopores of 

 medium size are usually found at the angles of junction of the walls. The 

 characters of this species as revealed by vertical sections are very like those of 

 Homotrypa communis, diaphragms being absent and the broken type of cysti- 

 phragms, so characteristic of that species, being well shown. 



The relationships of the present form, as already stated, are with H. com- 

 munis, but a decided difference from that species is indicated by the smaller 



