24 PALJEONTOLOGY OF NEW YORK. 



The sliell-substance in Lixgulops is exceedingly tenuous and not usually 

 resolvable into layers. The fossils are generally preserved as thin white films, 

 through which the thickened muscular area is plainly visible by its deeper 

 color. Its color alone indicates that its substance is largely if not quite cal- 

 careous, difl'ering from Lingula in this respect, but agreeing with Lingulasma 

 and the Trimerellids. 



Genus LINGULASMA, Ulrich. 1889. 



I'l.ATK II, FIUS. 17-23. 



1889. Lingulasvia, UuucH. Aineiican Geologist, vol. iii, No. (i, p. 383, figs. 5o, h, c, d (p. 378). 

 Compaj-e Lhiffula Canadensis, Billinos, ]S()2. Paleozoic Fossil.s vol. i, p. 114, fig. 9'). 



Diagnosis. Shell sub-quadrate, linguliform, sub-equivalve ; the brachial 

 valve considerably the deeper. Beaks apical, cardinal margins gently sloping 

 to the sides. 



Interior of the pedicle-valve with a low concave platform which extends 

 over one-half the length of the shell, and is not hollowed on its anterior wall. 

 The pedicle-area has been largely enclosed within the shell, making a distinct 

 sheath or shelf, beneath which lie the apical portions of the central and lateral 

 muscular scars. Crescentic scars scarcely defined. 



The brachial valve is deep, with a high platform of about the same extent as 

 that on the other valve, sloping inward near its anterior margin and continued 

 axially into a strong septum, which reaches nearly to the front of the valve. 

 Tlie anterior walls of the platform are broadly excavated, and close against the 

 base of the septum are hollowed out into short conical cavities. The crescent 

 is strongly developed and sharply pointed backward at its center, Its lateral 

 curves are broad, reaching to the edge of the platform. Directly in front of 

 its central angle lies a short, sharp, median ridge, which disappears near the 

 center of the platform. Lateral and central muscular scars well developed. 



Type, Lingulasma Schucherti, Ulrich. 



Observations. This remarkable form serves as a most important connecting 

 link between the paleozoic Lingulas and the Trimerellids, following, in the 



