SIS 
PALAEONTOLOGY OF NEW-YORK. 
Fig. 2 a, b. Dorsal and ventral views of the specimen, natural size. 
Fig. 2 c, d. Front and profile view of the same. 
Fig. 2 e, f. Dorsal and front views of a larger specimen, the lateral extremities of which 
are broken off. 
Geological position and locality. In slialy limestone of the age of the Lower 
Helderberg limestones : Decatur county, Tennessee. 
Trematospira camura. 
Plate XXVIII A. Fig. la - h . 
Mrypa camura : Falseontology of New-York, 1850, Yol.ii, pa. 273, pi. 56, f. 3. 
Shell transversely elliptical or subrliomboidal, sometimes depressed sub- 
globose (varying much in form according to age) : valves nearly equally 
convex. Ventral valve having a narrow well-defined sinus, which is 
usually marked by one or two plications smaller than those on the 
lateral portions of the shell, and which become obsolete before reaching 
the beak : beak elevated, small, acute, slightly incurved, and vertically 
truncate by a small round or slightly oval perforation, the louver side 
e 
of which is formed by a well-defined deltidium. Dorsal valve with a 
scarcely defined mesial fold marked by two smaller plications, whicli 
usually become obsolete before reaching the beak : beak closely in¬ 
curved beneath the deltidium. 
Surface marked by about four, five, or six plications on either side of the 
mesial fold and sinus, and concentrically crossed by imbricating lines 
of growth, with the entire surface granulose or punctate. 
This species varies considerably in its form and proportions; being sometimes 
depressed globose, with length and width 'about equal, while the prevailing forms 
have the width nearly one-half greater than the length. In a single individual, 
which does not appear to have been distorted, the width is twice as great as the 
length. In all these variations, it preserves the characteristic surface markings. 
Fig. 1 a. Dorsal view of a specimen of medium size. 
Fig. 1 b. Ventral view of the same, showing a,single .small plication in the mesial sinus. 
Fig. 1 c. Front view of the same. 
Fig. 1 cl. Profile view of the same. 
