NIAGAEA GHOUP. 267 



This species is evidently closely allied to D. elevata of Dalman ; but the apex is not 

 incurved, and in two specimens examined the foramen is narrow and linear, and filled by a 

 projecting callosity, unlike the representations in Dalman's figures. It is possible that a comr 

 parison of specimens, which I have had no opportunity of making, will show a more close 

 alliance than appears from the figure. 



This is an extremely rare species, two only having been seen. It is allied in form to a species 

 in the shaly limestone of the Helderberg, and to another in the Hamilton group, but is distinct 

 from either. 



Fig. 7 a. The ventral valve of this species. 



Fig. 7 b. Dorsal valve of the same. 



Fig. 7 c. Cardinal view, showing the area and long linear foramen which is closed. 



Fig. 7 d. Profile view of the same. 



Fig. 7 e. Several of "the plications enlarged, showing the concentric strias. 



Position and locality. The only two specimens seen were collected in 1837, from near the 

 top and just below the edge of the cliff on the Niagara river above Lewiston. It has not been 

 seen in any other locality, and is doubtless a very rare species. 



NOTE. 



TEREBRATULA, ATRYPA, HYPOTHYRIS, &c. 



In the present state of our knowledge, and in the divided or unsettled opinion of authors upon 

 this subject, I have preferred to allow the fossils of this family of the Brachiopoda to remain 

 under the Genus Atrypa, to which, strictly, many of them do not belong. I am averse to using 

 the name Terebraiula indiscriminately, according to most of the European continental authors : 

 neither does it appear well established tliat all the subdivisions proposed are tenable, or founded 

 upon structural characters of sufRcient importance. That the whole group requires a reorganiza- 

 tion, is but too apparent ; but we have, in attempting to introduce Deltsyris, Strophomena, 

 and other genera of Brachiopoda, occasioned, to beginners, more confusion and uncertainty than 

 advantage. These reasons, therefore, must be my apology for leaving, for the present, these 

 species under the Genus Atrypa. 



