FAMILY RHYNCHONELLID-^. 331 



FAMILY RlIli\€IIO^ELLID^. 



The Rhynchonellid.e are distinguished from the Spiriferid^ mainly 

 by the absence of calcareous spires; though Mr. Woodward includes 

 Atrypa in this family, remarking that the teeth and impressions are like 

 Rhynchonella, and that " the shells of this genus differ from Rhyncho- 

 " NELLA chiefly in the calcification of the oral supports, a character of 

 " uncertain value." Mr. Davidson and other authors have placed Atrypa 

 in the family Spiriferid^, and I see no reason for changing this disposi- 

 tion of the genus. The spires are in all respects similar to those of Spi- 

 RIFERA, the direction of their apices into the dorsal valve being simply a 

 feature of position. The muscular imprints are as much like those of 

 Spirifera as they are like Rhynchonella. 



Leaving out the Genus Atrypa, the Family Rhynchonellid^ will include 

 no genus with calcareous spires ; but from analogy with modern Rhyn- 

 chonella, they are supposed to have possessed fleshy spiral arms which 

 have not been preserved in the fossil state. This family, in its usually 

 accepted limitations, will include Rhynchonella (as at present under- 

 stood), Stenocisma, Leiorhynchus, Camarophoria , Pentamerus, and 

 Stricklandinia ; though I think there would be great propriety in 

 uniting the two latter genera with some others in a separate group. 



