isii PALJEOXTOLOGY OF NEW YORK. 



more nuiiRTous anil fosciculato at irregular intervals, proflucing a sligiitlv 

 luiilulated snrlace, crowded iiiid laniellose on the anterior. 



Interior iinkiKiwn. 



A specimen of a left valve lias a length, from hcak to hase, of 4o mm., 

 height 29 mm., and hinge-line to the base of the spine 'I'i mm. A right 

 valve, referred to this species, has a length of 32 mm., liciiilit 27 mm., and 

 hinge-line, exclusive of the .spine, 31 mm. 



This species is larger and more rohust tiiaii L. longispinum ; the body is wider, 

 less ol)liqne, and less abruptly recurving at the post-basal extremity ; the wing 

 is larger and the greatest depth of tlio sinus not quite so near the cardinal 

 line; the stride do not recurve so alirii|itly forward on the posterior slope; the 

 right valve is proportionally higher; the wing i.s less deeply sinuate, and the 

 spiniform extension is shorter. 



Compared with L. Morto«/, the body of the shell is less obliijuc ami moic 

 expanded, while the Aving is much smaller and the simis nearer the hinge-line. 



Furmalion and localitij. In the middle portion of the Chemung grouj) at 

 Painted Post, Steuben county, N. Y. 



LkI'TODESMA AgASSIZI. n. S|). 



n.ATK I,.\.\.\I.\, FIGS. 17-l!l 



Shell of medium size, sub-rhomboidal ; l)ody broadly ovate, obli»[ue to the 

 hinge-line at an angle of from 50'' to o5° ; length nearly one-third greater than 

 the height ; anterior margin broadly rounded below the In'ssal sinus; ventral 

 margin regularly curved ; more abruptly curved at the post-basal extremity. 



Left valve moderately convex below, more convex al)ove and gibbous on 

 the umbo, llight valve less convex. 



Hinge-line straight, about equal to the heiglit of tiie valve. 



Beaks snl)-anterior, scarcely directed forward, prominent, rising a little 

 aJKJve the hinge-line. Umboual region moderately gibbous, subtending an 

 acute angle. 



Anterior end large, obtuse, truncate above and curving below into the 



