GO 
PALAEONTOLOGY OF NEW YORK. 
the group without hesitation is quite 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 thoroughly 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 beyond 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 have 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 posterior portion, lies a 
central scar, not extending so far forward, but 
together with the lateral branches giving the 
entire muscular impression a strongly tripartite 
character. The 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 preservation, be resolvable into more detailed scars, but 
