8 UNITED STATES GEOLOGICAL SURVEY OF THE TERRITORIES. 



immediately within the beak of the ventral valve; and just in front of this 

 is the scar of the divaricator muscles (of Handcock — posterior adductors of 

 Woodward). At the anterior extremity of the visceral area, in the middle 

 of the same valve, are the four very unequal impressions of the posterior 

 adductor and external and central adjustor muscles (of Handcock), which 

 are so arranged as to impart a more or less trilobate outline to the anterior 

 margin of the slightly convex visceral area. Behind these, and just within 

 each lateral lobe of the visceral area, are situated, one on each side, the 

 widely-separated anterior occlusor scars ; and still farther back are seen, on 

 each side, those of the posterior adjustors, of which there are two on one 

 side, and one larger one on the other. 



In the dorsal valve there is no peduncular attachment, but. the scar of 

 the divaricator muscles is located nearly as in the other valve. The two 

 anterior occlusor impressions of this valve are placed in contact centrally, 

 side by side, at the farthest exterior extremity of the visceral area; and just 

 behind these, and a little separated from each other, are the two impressions 

 of the posterior occlusor muscles. About midway between the latter and the 

 posterior extremity of the visceral area are situated, near each lateral margin, 

 the small scars of the posterior external and internal adjustor muscles, of 

 which there are four on one side, and three on the other, one of the latter 

 being considerably larger than the others. 



This genus is nearly related to Lingulepis of Hall, and, so far as yet 

 known, only distinguished by the more attenuated beaks and much more 

 distinctly trilobate form of the visceral scar in the typical form of the latter. 

 There were, however, probably differences in the arrangement of the details 

 of the muscles in these two types that have not yet been determined, the 

 muscular impressions of Lingulejns being still unknown. 



Lingulella of Salter is another allied type that was separated from Liu- 

 gula chiefly on account of having a furrow extending along a kind of false 

 cardinal area to the beak of the ventral valve, as supposed, for the reception 

 of the peduncle. No such furrow has yet, I believe, been observed in any spe- 

 cies certainly known to belong to Lingulepk; but there are some reasons for 

 suspecting that this latter type may not be distinct, from Mr. Salter's Lingulella; 

 at least, I have seen a species agreeing with the latter in the. possession of the 

 false area and furrow, and yet showing, in the interior of the ventral valve, a 

 similar trilobate visceral scar to that seen in the corresponding valve of the 

 type of Lingulepis. (See Proceed. Acad. Nat, Sci. Philad., Oct., 1871, 185.) 



