CONTRIBUTIONS TO PALAEONTOLOGY. 187 



A variety (^A. crassa), which has not thus far aflforded the means of separation 

 as a distinct species, has the bases of the dental lamellae thickened, and extended 

 in strong ridges across the valve on each side obliquely to the anterior lateral 

 margins, leaving the central part of the shell of the ordinary thickness. 



Geological formation and locality. In shaly sandstone of the Chemung group, 

 crowded together in great numbers in some beds : Paintedpost, Jasper, Steuben 

 county; near Ithaca in Tompkins county, and in Chautauque county. 



VITULINA PUSTULOSA(n.s.). 



Shell plano-convex, semicircular : hinge-line equal or nearly equal to the greatest 

 width of the shell; area large, triangular, reaching to the extremities of the 

 cardinal line. Ventral valve highly convex, the greatest convexity at the umbo : 

 beak small, pointed, somewhat incurved over the area; foramen very broad, 

 equalling half the length of the cardinal line. Dorsal valve flat or slightly con- 

 vex, having a broad shallow sinus, flat or with an incipient fold in the bottom. 

 Surface marked by about ten moderately strong simple rounded radiating plica- 

 tions, two of which are slightly elevated in the middle of the ventral valve, in 

 form of a mesial fold corresponding to the sinus of the dorsal valve; the entire 

 surface beautifully covered with minute pustules resembling spine-bases. 

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



Hamilton group : Genesee county, N.York. 



SPIRIFER VENUSTUS (n.s.). 



Shell subrhomboidal, ventricose, length about two-thirds the greatest width : 

 hinge-line scarcely equalling the greatest width of the shell; ardi nal extremities 

 rounded. Dorsal valve very convex; mesial fold narrow above and expanded in 

 front. Ventral valve less convex than the opposite, broadly arching from the 

 extremities, the greatest convexity a little above the middle : beak arched; area 

 short, rounded, and not defined at the margins; foramen high, the height equal 

 to the width at the base; mesial sinus narrow and well defined near the beak, 

 broader below the middle and expanded in front, terminating in a broad tri- 

 angular extension. Surface marked by numerous fine bifurcating plications, the 

 mesial sinus margined by a stronger plication; at the beak there is a single one 

 in the centre which sometimes continues simple to the base, while the accessions 

 take place from the lateral ones, till there are 10, 11, or 12 within the limits of 

 the sinus near the base : plications crossed by arching lamellose strite, which 

 are granulose or fimbriate on the margins. 



This is one of the finest species of Spirifer in the Hamilton group, and equal 

 or superior in size and beauty to S. granulifera. It is the only species in this group 

 which has bifurcated plications, or plications on the mesial fold and sinus. The 

 largest specimen is about three inches wide, by nearly two inches long. In general 

 aspect and surface characters, this species resembles the finer specimens of S. ca- 

 meratus. 



Geological formation and locality. Shales of the Hamilton group : Livingston 

 county, N.York. 



TREMATOSPIRA GIBBOSA ( n. s.). 



Shell transversely subelliptical, once and a half as wide as long, ventricose, the 

 anterior margin thickened in old specimens; valves subequally convex. Beak of 



