217 
Pachydomus cypeina, J. D. Dana} 
PI. XVIII, Pig. 6. 
Astartila cyprina, J. D. Dana, 1817, Am. Journ. Sci., lY (2), p. 155. 
Idem, 1819, Geol. Wilkes’ U.S. Explor. Exped., p. 689, pi. 3, fig. 6 and 7 ? 
This shell is of moderate size, oval, thick, and very nearly one-third 
longer than hroad. Its beaks are thick, recurved, placed anteriorly, and very 
wide apart. The external surface is ornamented with closely crowded 
concentric strise; the internal surface is smooth except for some slight, 
irregular, transverse rugosities, and some indistinct folds beyond the pallial 
impression. The pallial impression is simple, and not far from the ventral 
margin. The muscular impressions are rather deep ; that of the anterior 
adductor is subquadrangular, while the posterior is oval ; both are superficially 
striated ; the imi^ression of the retractor of the foot is sigmoidal and smooth. 
Dimensions . — The length is forty-three, the breadth thirty-three, and 
the thickness thirty-one, millimetres. 
Relations and Differences . — By its size and general form this species 
resembles the preceding ; it differs from it by its measurements and by its 
muscular impressions. 
Horizon and Localities . — It is found with the preceding. 
Pachyuomus pusillus, F. McCoy. 
PI. XIX, Pig. 2. 
Fachydomus ? pnisillus, McCoy, 1817, Aun. Mag. Xat. Hist., XX, p. 302, pi. 16, fig. 1, 2. 
This is a small, suborbicular or globose shell, nearly as long as broad, 
with an arched hinge-line, and small, anterior, widely separated beaks. The 
anterior side is short and rounded ; the external ligament well developed ; 
the anterior muscular impression oval and deep, the posterior oval and super- 
ficial ; the pallial impression is entire ; and, according to Mr. McCoy, the 
lest is thick, and its surface covered with rugose, imbricated, concentric 
wrinkles. 
Dimensions . — The length is seventeen, breadth sixteen, and thickness 
fourteen, millimetres." 
^ [Dana’s genus Aaartila, classed here under Pachydomus, would apjiear to be valid. Stoliczka, Cret. 
Fauna S. India (Pal. Iiidica), 1871, pp. 274, 275 ; R. Etheridge, Junr., Geol. and Pal. Q'land, 1892, p. 277. — 
W.S.D.] 
^ I may state that these measurements were taken from a very perfect internal cast. 
