250 



ON THE TOPOGKAPHY AND GEOLOG^ 



C. circinata. Born, sp. , . - , ,. . : 



Vemis, id. Born, Test. Mus., p. 01, pi. 4, fig. 8. " " il / 



Uytlierea juncea. Giippy, Quart. Jour., Vol. XXII., p. 583, pi. §2, fig. 13. f 



Reeve is probably incorrect in referring tliis species to Mazatlan. There are West 

 Indian specimens in the Mus. Phil. Acad., which I have used for comparison.. 



CALLISTA. Poll. 

 C. plauivieta.. Giippy, Quart. Jour., Vol. XXII., p. 292, pi. 18, fig. 3.. 



C. acuticostata. Gabb, n. s. 



Shell rounded sub-triangular, beaks pointed, about' a third of the length from the anterior end which is excavated 

 above and prominently rounded below ; base regularly convex ; cardinal margin gently arched ; posterior end narrow ; 

 lunule minute, slightly sunken, internal margin entire. Surface covered with closely placed, acute, erect plates. 



In form this shell approaches 3f. juncea, but it is less convex, the lunule is very 

 much smallc)", it is more acutely pointed behind and the concentric ribs are more 

 numerous and have not the intermediate striation. . . ^ .. 



C. Carbasea. Gu^jpy, s}). ■ V ' 



Gytherea {Circe) Carbasea. Guppy, Quart. Jour., Vol. XXII., p. 292, pi. 18, fig. 13. . 



C. Tryoniana. Gabb, n. s. 



Shell rounded triangular ; beaks anterior ; cardinal margin arched ; base deeply convex ; anterior end narrowly 

 rounded, straight in the lunular region ; lunule large not sunken, bordered by an impressed line ; surface smooth in 

 the young, in the old covered by numerous small, rounded concentric ribs. 



A very little smaller than 3£ juncea, this shell differs markedly in its lunule and 

 surfaces and slightly in outline. It is more produced in front and more narrowly 

 rounded; in that species the lunular region is concave. 



CYCLIKA. Desh. ■ ' 



C. cyclica? Guppy, sp. . -l.^ ' 



Bosiiiia, id. Guppy. Quart. Jour., Vol. XXII., p. 582, pi. 22, fig. 15. 



I have a single shell about half the size of the one figured by Gupp}^, and which 

 differs slightly from his in outline. It is possibly a different species but I do not feel 

 warranted in proposing a new name on such insufficient material, especially since 

 I cannot get at the hino-e. ■ 



CARDIUM. Linn. 



0. (Trachycardium) s ub - e 1 on g a t u m . Sby., Proc. Zool. Soc, 1840. . ; ■ 



C. sub-elongaium. Rve. Icon., sp., 57. 'i 

 G. Uncjua-lconii. Guppy, Quar. Jour., Vol. XXII., p. 293, pi. 18, fig. 7. 



The Santo Domingo specimens agree perfectly with living shells from the sur- 

 rounding waters. 



C. (T. ) D u m i n i c e n s e . Gabb, n. s. 



Shell elongate, cordiform, convex, thin ; umbones prominent ; surface ornamented by nearly GO small sub-sciua- 

 mose ribs, the lateral ones bearing minute tubercles ; edges serrate. . . 



Of the size and form of C. suh-cJongatum, this species differs in being much 



