Gbabau — Faunas of the Hamilton Group. 



255 



is uniformly arcuate in various degrees from beak to posterior margin, the 

 amount of arcuation depending on the point of measurement. Anterior end 

 small, scarcely extending beyond the Deak, rounded, separated from the rest 



Figs. 1, 2. Goniophora modiomorphoides, gp. n. 



of the shell by a well-marked oblique sinus which extends from the beak to 

 the ventral margin where it causes a constriction in the margin. 



Test ornamented by numerous strong, regular, subimbricating lines of 

 growth, which are abruptly deflected at the umbonal slope, continuing at a 

 slightly acute angle, and becoming more curving towards the cardinal margin. 



Anterior muscular impression subcircular, pronounced. Other internal 

 characters not observed. Three specimens of the ordinary size measure: 62, 

 57, and 58 mm. in length, by 37, 36, and 34 mm. in height. A small 

 specimen measures 41 mm. in length by 24.5 mm. in height. 



This species differs conspicuously from all the other Hamilton species in 

 its regularly arcuate umbonal ridge. In general appearance it recalls the 

 form of some of the common species of ModiomorpAa, especially M. concert- 

 trica, which it resembles in the regular striae, the anterior subnasute end, the 

 well-marked sinus, and the arcuate umbonal ridge. The angularity and 

 distinctness of this ridge in the present species distinguish it at once. The 

 specific name is intended to express this similarity. 



The type specimens were obtained from the upper part of the Encrinal 

 limestone, where they are associated with MbdiomorpJia concentrica and other 

 species. In the limestone specimens, the test is seldom well preserved, and its 

 thickness cannot be ascertained. A specimen in shale from the lake shore is 

 referred to this species. Two specimens from the Encrinal limestone show a 

 greater angularity in the umbonal ridge which is almost crested. The poster- 

 ior slope is more oblique and more direct. 



