CONTRIBUTIONS TO PALEONTOLOGY. 23 



very regularly rounded; cardinal slopes abrupt, nearly straight : 

 substance of shell very thin. 



Surface marked by extremely fine concentric striae, and, below the 

 centre of the shell, by numerous undulations, which are stronger 

 on the middle and become obsolete on the sides. 



In the ventral? valves, a strongly impressed linear indentation marks 

 the centre of the shell from near the beak more than halfway to 

 the base. This feature is observed in the best specimens seen, as 

 well as in partial casts. An apparently adult specimen measures 

 nine-tenths of an inch in length, and five-tenths in the greatest 

 breadth. 



This species differs conspicuously from all others of the Hamilton and 

 Chemung groups, except the L. maida, which is proportionally shorter, 

 with more attenuate cardinal extremity and stronger surface striae. 



In general form, this species bears some resemblance to Lingula ovata 

 of M'CoY ( British Palasozoic Fossils, PI. 1 L, f . 6 ), having the same 

 slender form ; but the sides are not so straight, and the front is more 

 curved. It has not, however, the robust form of that species as represented 

 in figure 1, Plate iii, of the Synopsis of the Palaeozoic Fossils of Ireland. 



Geological formation and locality. In the shales of the upper part of 

 the Hamilton group, near Canandaigua lake. 



*' LINGULA ALVEATA ( n. s.)." 



Shell subelliptical ; sides curving, broader below the middle, 

 somewhat abruptly expanding and curving from the beak for 

 more than one-third the length of the shell. 



Two separate valves examined (one of them a cast), are flat, and 

 have a somewhat elevated or thickened border, extending from 

 the beak, within which is a distinct groove nearly parallel with 

 the margin and reaching half the length of the shell : the centre 

 is marked by a longitudinal linear impression for more than 

 half its length ; and the cast of one specimen preserves the 

 mark of a thin septum, which extends from just beneath the 

 beak three-fourths the length of the shell. 



One specimen is nearly an inch and a half long, and the other one inch 

 and one-eighth. The thickened border and thin median septum are distin- 

 guishing features. 



There are some peculiarities in these specimens, which lead one to sup- 

 pose that a full knowledge of their characters and interior structure may 

 authorise their separation from the ordinary forms of Lingula. 



Geological formation and locality. In the shales of the Hamilton group, 

 Ludlowville, Cayuga county ; and in a sandstone near Fultonham, Scho- 

 harie county. 



