25 



size of the tubes and by the absence of maculae of any kind. It perhaps resembles 

 H. austini,. Bassler, still more closely, but differs in having the cystiphragms 

 distributed evenly throughout the peripheral zone, whereas in that species 

 they are confined to the maculae. 



Locality. — Credit river, Streetsville. 



Nos. 12163, 12164, 12165, Royal Ontario Museum of Paleontology. 



HOMOTRYPELLA EXPANSA, Sp. UOV. 



Plate V, Figure 11 



A specimen was found in the Streetsville collection of Bryozoa in the Royal 

 Ontario Museum of Paleontology, which in its internal characters resembles 

 Homotrypella hospitalis (Nicholson), very closely. The growth, however, 

 is vastly different from the typical growth of the latter species, the zoarium 

 being a broad, undulating expansion, 90 mm. in diameter, with an average 

 thickness of three millimetres instead of a sub-hemispheric, sub-conical, or 

 irregular compact mass. In places the expansion consists of a single layer, 

 in other places of two or more successive layers. Over the surface are evenly 

 distributed low but distinct monticules, which consist of tubes somewhat larger 

 than average in size. 



The presence of monticules and the peculiar form suggest that the species 

 might be referred to the genus Monticulipora, but it has been retained in the 

 genus Homotrypella on account of its very close similarity, internally, to H. 

 hospitalis, and because the walls are clear and definite in structure. Bassler 

 states that one of the best features for the determination of the genus Monti- 

 culipora is the hazy, indefinite character of the walls. 



Locality. — Credit river, Streetsville. 



No. 254, Royal Ontario Museum of Paleontology. 



Homotrypella hospitalis peculiaris, var. nov. 

 Plate IV, Figure 1 



Monticulipora (Prasopora) Selwynii, var. hospitalis, Nicholson. Genus Monticulipora, 



1881, p. 209, fig. 45. 

 Prasopora hospitalis, Cumings. 32nd Rep. Dept. Geol. Nat. Res. Indiana, 1908, p. 871, 



pi. 23, figs. 1, lb'; pi. 31, fig. 6. 

 Homotrypella hospitalis, Bassler. Bull, U.S. Nat. Mus., 77, 1911, p. 174 (gen. ref.). 



The original description of Homotrypella hospitalis appears below: — 



M. selwynii var. hospitalis is invariably an attached form, all the numerous examples which' 

 I have seen being fixed to the exteriors of the shells of brachiopods. In form they are hemispheric, 

 rarely nearly globular, and their general size is from six to ten lines (about 12 to 20 mm.) in 

 diameter and from three to four to seven or eight lines (6 to 16 mm.) in height. 



Tangential sections show a close correspondence in general structure with the type form of 

 M. selwynii from the Trenton Limestone. The corallum (zoarium) is composed of large and 

 small corallites (zooecia) the former being oval or circular in shape and varying from 1/50 to 

 1/70 of an inch in diameter (four to six in two millimetres), each showing an excentrically 

 perforated tabula (diaphragm). The small corallites (mesopores) are numerous, sub-angular 

 and wedged in between all the larger tubes occasionally being aggregated into star-shaped groups 

 or maculae. 



Besides the normal two kinds of corallites, a considerable number of thick- walled, hollow 

 spines (acanthopores) may be observed which I have not detected as present in the examples 

 from the Trenton Limestone. 



Vertical sections show the same marked difference in the tabulation of the large and small 

 corallites as has been previously noticed in the type form with some differences. The large 

 tubes are always doubly tabulate, one set of tabulae forming a series of large lenticular vesicles 

 (cysts) while the remaining tabulae are horizontal and remote. The small corallites are furnished 

 with numerous complete horizontal tabulae. 



