142 GEOLOGY AND PALEONTOLOGY OF THE WEST INDIES. 



One poorly preserved specimen is doubtfully referred to P. nugenti. 



Locality. — Hodge's Bay, Antigua, station 6862, Vaughan. 



Geologic horizon. — Oligocene. 



Cotypes — Phila. Acad., No. 1656. 



Figured specimen. — U. S. Nat. Mus. No. 167067. 



Pecten species. 

 (Plate 13, Figure 4.) 



The Vaughan collection contains a fragment of a Pecten, probably 

 new, which is very convex and when entire had probably about 25 

 round ribs with equal interspaces. It has a concentric sculpture of 

 close raised lines. The margin is fluted within in accordance with the 

 external ribbing and set with paired raised lines corresponding to the 

 interspaces. These raised lines end abruptly at a distance of about 2 

 mm. from the margin, but are continued on the inner layers of the shell. 



Locality. — Willoughby Bay, Antigua, station 6881, Vaughan. 



Geologic horizon. — Oligocene. 



Figured specimen.— U '. S. Nat. Mus. No. 167132. 



Pecten (Amusium) lyonii (Gabb.) 



(Plate 13, Figures 1 a, 6, 2.) 



Pecten mortoni Guppy, Geol. Mag., Dec. 2, vol. 1, p. 443, 1874. (Not of Ravenel.) 

 Pleuronectia lyonii Gabb., Jour. Acad. Nat. Sci. Phila., 2d ser., vol. 8, p. 347, plate 45, figs. 



25 a, b, 1881. 

 Amusium lyoni Dall, Trans. Wagner Inst., vol. 3, pt. 4, p. 719, 1898. 



The following is a description of this species : 



Shell orbicular, thin, compressed; nepionic shell with about 24 small 

 rounded ribs which disappear on the adult shell; ears large, equal; right valve 

 a little more inflated than the left, evenly convex, smooth; left valve nearly 

 flat, with a broad, shallow, radial depression from beak to margin at the 

 posterior quarter and a very faint corresponding depression at the anterior 

 quarter; left valve with concentric sculpture of fine, impressed lines, between 

 which the shell is sometimes slightly convex; hinge-line nearly straight; sub- 

 margins very narrow; interior of the shell with low, equidistant ribs; paired 

 peripherally. 



Alt., 54 mm.; lat., 56 mm.; diam., 13.5 mm. 



This shell is very like Amusium precursor Dall, from the Chipola 

 Oligocene, but that species lacks the nepionic ribbing, which appears 

 to be a constant feature of the Anguillan form. A. mortoni Ravanel is 

 quite distinct, being proportionately higher and having a smooth 

 nepionic shell. 



This species is referred to A. lyonii on the authority of Dr. W. H. 

 Dall, who has identified a right valve in the Guppy collection with 

 Gabb's shell. It is possible, however, that comparison of the left valve, 

 which possesses more identifiable characteristics than the right, will 

 show this species to be distinct from the Costa Rican form. A left 

 valve from 70 km. west of the terminal of the Tehuantepec Railway, 



