Grabau — Faunas of the Hamilton Group. 



283 



130. Camarot(echia, sp. 



A single pedicle-valve with few, distant, and rounded narrow plications, 

 found in the Encrinal limestone, has the plications deeply bifid at the front 

 and there are apparently but two in the sinus, and four on either side 

 of it. The general form is like that of C. Sappho, but the interspaces are too 

 wide and the sinus too shallow, to allow its being referred to that species. 



Genus Liorhynchus, Hall. 



131. Liorhynchus multicostus, Hall. 



1867, Hall, Pal. N. Y., vol. 4, p. 358, pi. 56. 



This is the most abundant rhynchonelloid shell in the Hamilton group 

 of this region. It occurs throughout the group, but is usually restricted to 

 special layers, where it is often found in such abundance that one specimen 

 obliterates the characters of the other. It occurs sparingly in some of the 

 lowest beds, but becomes more abundant farther up, especially where concre- 

 tionary masses occur in the shale. It continues abundant up to about four- 

 teen feet below the Encrinal limestone, after which it becomes very rare 

 and practically disappears for a time, reappearing again in the lower Moscow 

 shales where it is at first rare. It becomes somewhat more abundant 

 as we ascend, until within about a foot or two of the top it has become 

 extremely abundant again. At this level also occur large specimens 

 which have the lateral plications rather indistinct, and only three plica- 

 tions in the sinus, also a number of small, flat, scarcely plicated shells 

 which must be referred to this species. The whole tendency in the spec- 

 imens from these shales is towards an approximation to the features of 

 L. qiiadricostatus of the Genesee slate, and occasionally a specimen is found 

 which is practically indistinguishable from that form. The specimens from 

 the concretions usually show the normal characters of the species, as do also 

 many of the specimens from the shale. The plications in these are well 

 developed on the lateral slopes, becoming, however, obsolete towards the beak. 

 In rare cases do they reach the beak. Bifurcation is common in the plications 

 of the fold and sinus, and is not infrequent in those of the lateral slopes, 

 especially near the top. The specimens from the limestone concretions are 

 usually somewhat smaller than those from the shale. 



