48 CONTRIBUTION TO THE PALEONTOLOGY OF TRINIDAD. 



those mentioned, but it is too incomplete for description. The hinge teeth are, 

 however, perfectly preserved and show that the shell was unquestionably an 



Area, 



Geological horizon. — Oligocene. 



Genus CUCULUBA Lamarck, 1801. 



Cuculhea harttii Rathbun. Plate VIII, Figure 12. 



Area ( Cucullcea t) Harttii Rathbun, Proc. Boston Soc. Nat. Hist., vol. XVII, pp. 248-249, 1875. 

 Cucuttaa (Idonearca) harttii White, C. A. Archivos do Museu Nacional do Rio de Janeiro, vol. 



VII, p. 65, pi. V, figs. 7, 8, 1887. 

 Cucullasa harttii Harris, Bull. Amer. Paleont., vol. I, p. 154, 1896. 

 Cucullaa harttii Branner, Bull. Mus. Comp. Zoology, Harvard College, vol. XLIV, p. 13, 1904. 



Rathbun 1 s original description.—" Shell of medium size, elongate, gibbous, 

 with the height nearly two-thirds the length. Outline of internal mould sub- 

 ovate, the height of the posterior extremity being much greater than that of the 

 anterior. The beaks are situated at a little more than one-third the length from 

 the anterior margin, are very prominent and incline strongly forward. Hinge 

 nearly as long as the shell. The posterior margin extends obliquely downward 

 and slightly backward, rounding strongly toward the ventral margin. The 

 anterior margin leaves the hinge abruptly, at nearly a right angle, and curves 

 rapidly round to the ventral margin, which is slightly rounded and descends 

 moderately in extending backward. The valves are very convex and arch 

 strongly from the beak to the ventral margin. The depth of each valve is more 

 than one-third the height of the shell. The posterior slope commences abruptly, 

 along a line extending from just behind the beaks to the lower posterior corner 

 and descends rapidly to the hinge and posterior margin. This slope is broad, 

 quite concave just back of the beaks, but becomes nearly straight posteriorly. 

 The surface is marked by small, rounded or subangular radiating raised lines, 

 which are very fine at the beaks, where they are of about the same width as 

 the interspaces, or narrower, and increase very gradually in size toward the 

 margin, the interspaces there being much the narrower and even reduced to mere 

 striae. Fine concentric lines cross the shell ; on the upper portion of the shell 

 they are very regular, but near the ventral margin they become more numerous 

 and are crowded together. As they cross the radiating lines they become very 

 prominent, sometimes giving to the latter a beaded appearance. On the posterior 

 slope the radiating lines are minute, threadlike and near together, being separated 

 by very narrow depressions. These seem to be made even more beaded in 

 appearance by the concentric lines than are the radiating lines on the main portion 

 of the shell, though they are exceedingly fine. The inner margin of the shell is 

 crenulated. 



" The shell is quite a thick one, and none of the exterior characters appear in 

 the interior, so that the angular appearance presented by the external moulds 

 is not apparent in the very numerous interior ones. The characters of the interior 

 are quite obscure in all the specimens obtained rendering the determination of 



