20 



before the surface is reached. There is no definite boundary between the 

 mature and submature regions, but one fades gradually into the other. 



Hallopora aequalis differs from Hallopora onealli creditensis, the only other 

 species on the Credit river for which it might be mistaken, in the manner in 

 which the mesopores pinch out at the surface, resulting in the polygonal shape 

 of the apertures in the former, while in the latter species the zooecial apertures 

 are rounded or oval, with numerous mesopores between them. 



H. aequalis resembles H. onealli communis (James) in the manner in which 

 the mesopores pinch out at the surface, but differs distinctly in having no 

 maculae, in having smaller tubes, and by the fact that the branches do not 

 appear to form bushy masses by anastomosis as in the case of H. onealli communis. 



Bassler in his study of the James types of bryozoans makes a few comments 

 on H. onealli communis, but does not infer that "maculae or monticules occupied 

 by calices much larger than the average occur in most specimens" as stated by 

 James in the original description of the same species. If it is true that the 

 presence of maculae is not a varietal feature in H. onealli communis, then our 

 species differs from it chiefly in the smaller size of the tubes. 



Locality. — Credit river, Streetsville. 



No. 12150, Royal Ontario Museum of Paleontology. 



Hallopora maculosa, sp. nov. 

 Plate II, Figures 3 and 4 



A single specimen of Hallopora was found in the Stromatocerium reef in 

 which the arrangement of the mesopores is very peculiar. Instead of being 

 mo,re or less regularly distributed throughout the zoarium, as in all other species 

 of Hallopora which have been studied for this paper, the mesopores are confined 

 to maculae in each of which they occur to the number of 15 or 20. In the 

 features shown by the vertical section, H. maculosa does not differ from H. onealli 

 or the variety of that species so common on the Credit river, H. onealli creditensis. 



Very little of the specimen was left after the sections were made; in con- 

 sequence, the general shape of the zoarium cannot be described. Vertical 

 sections, however, show that the specimen had grown over the ramose zoarium 

 of another species of Hallopora, indicating a probable encrusting habit. It is 

 hoped that further search will yield other examples of this species, which will 

 serve for further description as to structure and manner of growth. 



Locality. — Credit river, Streetsville. 



No. 12151, Royal Ontario Museum of Paleontology. 



Hallopora onealli creditensis, var. nov. 

 Plate I, Figure 8; Plate V, Figures 6 and 7 



A form of Hallopora is abundant in the Credit member and at various levels 

 in the Erindale and Streetsville members, which closely resembles Hallopora 

 onealli sigillarioides (Nicholson) of the Eden, forming branching stems with an 

 average diameter of 4.5 mm. It also resembles that species closely in internal 

 characters, but is given a new varietal name partly on account of one small 

 internal difference and also because of the much higher horizon at which it is 

 found. No sign of larger tubes has ever been seen in the Credit River variety; 

 a feature which is often present to some extent in H. onealli sigillarioides. 



