128 GEOLOGY AND PALEONTOLOGY OF THE WEST INDIES. 



A single fragment was collected by Dr. Vaughan, in whose honor the 

 species is named. It is broken at both ends and has been rendered 

 somewhat unsymmetrical by pressure, which has also increased the 

 acuteness of the carinal angles. 



This species is not unlike P. carnea Gmelin, but that species has 

 rudimentary riblets on the lower part of the ventral area. 



Locality. — Crocus Bay, Anguilla, station 6894, Vaughan. 



Geologic horizon. — Oligocene. 



Type.—U. S. Nat. Mus. No. 167047. 



Ostrea antiguensis Brown. 



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



Ostrea antiguensis Brown, Froc. Acad. Nat. Sci. Phila., p. 614, plate 19, fig. 7; plate 20, 

 figs. 1, 5, 6; 1913. 



The following is the original description of this species: 



"Shell ovate or nearly orbicular, thick and dense, externally radially plicate 

 or sometimes nearly smooth, the plications on the lower, deep valve begin 

 at the beak and are usually seven in number, of which a group of five ridges 

 is separated from the other two by a broad depression; the ridges sharp and 

 spinose or obtuse and even, the furrows or depressions smooth and rounded. 

 Hinge moderate, the shell rapidly widening beyond the end of the hinge line, 

 the plications usually dying away as the margin of the adult shell is reached, 

 and this margin in the lower valve being turned up abruptly for one-half inch 

 or more, making a cup-shaped valve. The muscle impression is distinct, more 

 strongly impressed in the case of the deep valve; situated on the left and 

 nearer to the beak than to the opposite margin. The lower valve is more or 

 less excavated internally, the upper valve is flat. When strongly plicate and 

 even spinose, this species closely resembles 0. gatunensis B. and P., except 

 that this latter species has not the heavy shell of 0. antiguensis nor has it the 

 tumed-up margin. 0. haitensis Sowb. has the rugose exterior of this species 

 in its strongly plicate form, but while the shell is heavy, it lacks the upturned 

 edge of 0. antiguensis. Length 85 mm., alt. 80 mm., depth of lower valve 

 30 mm. 



"In size and plication 0. antiguensis varies largely, but of the specimens 

 collected the longest shells do not run far from 90 mm. in altitude. As regards 

 plication, some are nearly smooth and some are strongly rugose, even in some 

 cases spinose, but all may be distinguished by the broad furrow which runs 

 across the exterior of the lower valve about opposite to the muscle impression 

 and which divides the rugse into a group of five and one of two. The species 

 differs also from all other closely related American species by the upturned 

 margin of this lower valve and the correspondingly reflexed margin of the 

 upper or flat valve." 



This is a heavy, massive species, resembling, in that respect, 0. 

 podagrina Dall. The broad depression on the lower valve, although 

 usually present, is not a constant feature, but is occasionally absent, 

 even on plicate individuals. A rather persistent character is a long, 

 crescent-shaped excavation on the interior of the lower valve, extending 

 practically the entire length of the shell. The upturning and reflexing 

 of the margins, mentioned by Professor Brown, is not a noticeable 

 feature of the specimens in the Vaughan collection. 



