254 



ON THE TOPOGliAPIlY AND GEOLOGY 



original specimen in the comparison. We have therefore another supposed extinct 

 species bronght to light on onr Gnlf coast. 



A. imbriccata . Brug., Enc. Metli., 1789, p. 98. 



A. Americana. D'Orb. (not Gray), La Sagra, pi. 28, fig. 1-2. • ' 



A. Noce. Guppy (not Linn.), Quart. Jour., Vol. XXII., p. 293. 



Brugiere's species is said by Reeve to come from the East Indies. There are 

 recent specimens of this sj^ecies in the Mnscnm Philadelphia Academy, labeled St. 

 Thomas, and on comparing them with the description in Icon. Conch, (the figure is 

 valueless), they agree in eveiy detail. D'Orbigny's name is preoccupied by G-ray, so 

 the species must either be called by Brugiere's name, or there is an opportunity for 

 somebody to propose a new one. I do not feel warranted in separating it from A. im- 

 hricata^ unless the West Indian shell should prove different from the Oriental. 



A. ( Auadara) P e n n e 1 1 i . Gabb. 



Shell sub-quadrate, Avidening posteriorly, very oblique ; beaks a little less than a third of the length from the 

 anterior end, approximating ; area very narrovF, wider in front of the beaks than behind ; base convex, sloping up- 

 wards continuously with anterior end ; posterior end broadly rounded sub-truncate ; surface marked by about 35 

 square ribs, slightly beaded in the young shell. Length 1.4 inch, width 1. inch, diameter 1.05 inch. 



The most abundant of the Santo Domingo A.rcas, this species can be at once dis- 

 tinguished by its oblique and very convex form. It is nearest to a shell which I find in 

 the Museum Philadelphia Academy, labeled A. lohata, Rve., but which I cannot find 

 in the books. It is more oblique and more convex than that species, with the beaks, 

 more anterior. That has 28 ribs, while this has 35. In this the ribs are of uniform 

 size, while in that species the posterior ribs are broader than the others. 



learned after Mr. A. Pennell, the chief topographical assistant in the survey. 



A. multilineata. Gabb, n. s. 



Shell small, obliquely oval, very convex, length and breadth about equal ; beaks small, anterior, approximate, 

 hinge line a little shorter than the sliell, area broad in advance of and under the beaks, very narrow behind ; posterior 

 end broadly rounded ; base convex and curving upwards regularly to the anterior end ; surface ornamented by about 

 CO small square ribs, slightly crenulated by sub-squaniose lines of gi-owtli. Hinge composed of regular transverse 

 teeth, those of the two ends radiating outwards. Internal margin not crenulated. 



A little less than a half inch in diameter, recognizable by its thin globose shape 

 and its numerous riljs. In this latter character it approaches A. centenaria among the 

 recent forms, l)ut it differs from that in its rounder form. It is also allied to some of 

 the Ci-etaceous species. 



I BARB ATI A. Gray. - , V ." . . : 



I B. B 0 n a c z y i . Gabb, n. s. j • . ■ . . 



Shell elongated, compressed ; very inequilateral ; beaks barely more than a fourth of the length from the anterior 

 end ; approximating ; nmbones broad ; hinge line moderately long ; anterior end rounded ; j)osterior end produced, 

 sloping above ; base undulated, area long and narrow. Surface marked by numerous small radiating ribs ; more or 

 less grooved and sometimes minutely beaded. Length 1.5 inch. * 



