PARYPHORHYNCHUS 187 



The minute surface markings of the shell are preserved in none of the 

 specimens studied, but concentric lines of growth, irregular in strength 

 and distribution, are present upon all specimens examined. 



Remarks. In its external form this species most closely resembles 

 Skumardella obsolens, but it always grows to a much larger size and may 

 be recognized by that character alone. Internally the two forms are 

 quite distinct, L. greenianum having the hinge plate of the brachial valve 

 completely divided, with the space between the two divisions of the 

 median septum much broader, and the septum reduced in height much 

 more rapidly. Both the internal characters and the external form agree 

 with the genus Liorhywchus, in which genus the species is placed un- 

 hesitatingly. 



Horizon. Knobstone formation, Indiana. 



Genus PARYPHORHYNCHUS Weller 



Description. Shells rhynchonelliform, of medium size or larger, sub- 

 ovate to transversely subrhomboidal in outline, mesial fold and sinus 

 well developed, both valves marked by broad, rounded plications, which 

 reach nearly or quite to the beak, surface of both valves also marked by 

 fine, radiating stria? which cover both the plications and the intervening 

 furrows. The internal characters of the rostral portion of both valves 

 entirely similar to Camarotoechia. 



G 



FIG. 8. A series of seven cross-sections of the rostral portion of the shell of 

 Paryphorhynchus elongatum (X 2 1 /), showing the dental lamellae of the 

 pedicle valve and the median septum, crural cavity and crura of the brachial 

 valve. 



Remarks. In the arrangement of the internal structures of the rostral 

 portion of the shell in this genus, there is nothing to differentiate it from 

 Camarotcechia. The essential generic features are found in the external 

 characters, viz., the broad plications and especially in the finely striate 

 shell surface, in association with the camarotoachoid interior. 



