60 PALAEONTOLOGY OF NEW YORK. 



the group without hesitation is (juite small, and if the generic features of the 

 type-species L.pinniformis, are strictly adhered to, it may be necessary to restrict 

 the specific representation to very narrow limits. The original species is the 

 most thorough-ly understood in both exterior and interior details. The ex- 

 ternal character of the shell itself, when both valves are present, allows of 

 a ready distinction from all known forms of the genus Lingula. The pedicle- 

 valve bears a long, attenuate rostrum, which extends far ])eyond the apex of 

 the opposite valve. This appears to have been open on the lower side for its 

 entire length, for the passage of the pedicle, though we have no conclusive evi- 

 dence that it may not luive been partially covered by a thin deltidium of similar 

 character to that in Lingula anatina. The brachial or dorsal valve is broadly 

 ovate in outline, having an obscure beak and a general form which would be 

 in precise agreement with that of the opposite valve, were the rostrum of the 

 latter truncated at its base. The separated valves of L. pinniformis occur in 

 great quantities in the Potsdam sandstone at the Falls of St. Croix, Min- 

 nesota and Wisconsin, crowded together to the exclusion of any other fossil, and 

 there can be no doubt that the valves described in the Sixteenth Report of the 

 State Cabinet of Natural History, as dorsal and ventral, are such, although no 

 specimen has been seen in which the valves are in their natural juxtaposition. 

 The muscular impressions of the pedicle-valve may be determined with 

 tolerable accuracy. A single large scar, occupying the entire umbonal region, 

 is produced anteriorly into two narrow lateral 

 branches, extending for about one-half the 

 length of the shell. Between them and con- 

 tinuous with their po.sterior portion, lies a 

 central scar, not extending so far forward, but 

 together with the lateral branches giving the 



.. 1 . . , , , . ,. FrGS 'JJ. 23. Lingulepis pinniformis. 



entire muscular impression a strongly tripartite M.nterai sc.ais. c, ctntiai. s, septum. 

 character. Tlic homology of these scars with those of Lingula is not readily 

 apparent, although there is a degree of similarity which is quite strongly shown 

 in the outline of the central scars. Probably the entire muscular impression 

 would, under perfect preservntion, be resolvable into more detailed scars, but 



