26 



Cumings {op. cit.) states that:- 



In form H. hospitalis is fairly typical, although rather more inclined to form irregular 

 masses than its Trenton relatives which are usually very regularly hemispherical or sub-conical 

 in form. 



H. hospitalis is abundant in all the subdivisions of the Richmond formation 

 on the Credit river, with the exception of the Queenston. At times it forms 

 very regular, hemispheric or sub-conical zoaria, while at other times the zoaria 

 are very irregular in shape (Plate V, Figures 1 and 2). In addition, a few 

 specimens have been ascribed to a new variety. 



H. hospitalis peculiaris differs from the type in one feature only, namely, 

 in the possession of numerous minute acanthopores, which are situated along 

 the zooecial walls between the large acanthopores characteristic of the type. 

 These small acanthopores are much more pronounced near the surface of the 

 zoarium, where as many as six have been counted between two large acantho- 

 pores. Deeper in the zoarium they may disappear altogether. They are 

 apparently of the nature of true acanthopores since hollow centres have been 

 seen in many instances. 



Locality. — Credit river, Streetsville. 



No. 12166, Royal Ontario Museum of Paleontology. 



MONOTRYPELLA CURVATA, Sp. flOV. 



Plate IV, Figures 3 and 4; Plate VI, Figure 3 



This species is represented by a single specimen, which was found among 

 the Townsend collection of Streetsville fossils in the Royal Ontario Museum 

 of Paleontology. The exact stratigraphic level from which it came is not 

 known, but it was probably from the Columnaria reef of the Meadowvale member, 

 since a fragment of Columnaria calicina, a species very common in the reef, was 

 found adhering to the zoarium. In form it is an irregular, sub-ramose mass, 

 35 mm. in length and 25 mm. in diameter, with a smooth surface. 



Tangential sections show the zooecia to be of large size, six occurring in 

 two millimetres. A few small tubes are scattered among the larger ones which 

 are probably not of the nature of mesopores as no evidence of the presence of 

 two types of tube is seen in vertical sections. The zooecial walls are compara- 

 tively thick near the surface, but are much thinner in sub-mature regions. 

 The line of demarcation between adjacent tubes is very distinct and there is a 

 total absence of acanthopores. 



In vertical sections, numerous well-defined diaphragms are seen crossing 

 the tubes. They are in most cases considerably curved and approach the 

 funnel-shaped diaphragms of Amplexopora robusta, Ulrich. These curved 

 diaphragms appear in tangential sections as complete rings, within the walls 

 of the zooecia. 



M. curvata differs from other members of the genus in the curved diaphragms 

 and the large size of the tubes. It resembles Amplexopora robusta in some 

 features but differs in the absence of groups of larger tubes and in the absence 

 of acanthopores. 



Locality. — Credit river, Streetsville. 



No. 12167, Royal Ontario Museum of Paleontology. 



