274 
PALAEONTOLOGY OF NEW-YORK. 
Trematospira hirsute. 
PLATE XLV. 
Jtrypa hirsuta : Hall, in Tenth Report on the State Cabinet, p. 108. 1857. 
Trematospira hirsuta : In. Thirteenth Report on the State Cabinet, p. 101. 1860. 
Athyris (?) chloe : Billings, Canadian Journal, p. 282. 1860. 
Shell depressed-orbicular in the young state; becoming subtrilobate by 
the gradual development of a mesial fold and sinus, and often gibbous 
in the older specimens ; valves subequally convex; hinge-line extend¬ 
ing about two-thirds the width of the shell. 
Ventral valve usually a little more gibbous than the opposite; greatest 
convexity above the middle of the shell, whence it curves regularly to 
the apex, which is terminated by a circular foramen, or more often 
truncated below by the summit of the opposite valve : contour, regu¬ 
larly curving to the cardinal and lateral margins. The mesial sinus 
becomes gradually developed above the middle in full grown shells, 
and is very conspicuous towards the front, having the sides curving 
and rarely strongly defined. The false area is not visible beneath the 
beak. 
Dorsal valve regularly convex in young shells; becoming elevated in 
the centre, and a mesial fold gradually developing itself, till in old 
shells it becomes very conspicuous towards the front. The sides -are 
pretty regularly convex, and curving towards the margins. 
Surface marked by from thirty to forty simple low rounded striae, which 
are obscure towards the beaks, but become larger and more conspicuous 
towards the margin : these are crossed by fine close concentric lines 
of growth, and more distant imbricating lamellae. The surface ordi¬ 
narily preserved is granulose; but when perfect, it is covered by 
minute seta or spinules, the bases of which, remaining, give the papil¬ 
lose character. Entire shell structure punctate. 
The interior of the ventral valve shows two strong teeth, which are 
extended in low plates along the sides of the rostral cavity to the mar¬ 
gins of the muscular area, which is broad, flabelliform, and scarcely 
defined on the front and lower lateral margins. 
