614 PROCEEDINGS OF THE ACADEMY OF [NoV.^ 



Orbitoides, etc., Oligocene. Cotypes A. N. S. P. Collection, inverte- 

 brate fossils, No. 1,648. 



Pecten nugenti n. sp. Plate XIX, figs. 2, 5, 6. 



Shell inequivalve, oval in outline, with 17 distinct rounded radial 

 ribs (and probably 2 additional less distinct ones) separated by 

 narrower interspaces, the whole exterior surface covered by concen- 

 tric growth lines which are raised and produce a nearly microscopic 

 sculpture extending equally over ribs and interspaces. Internally 

 smooth, except near the margin, where raised ribs are seen, occupying 

 the intervals between the raised external ribs. On the flatter valve, 

 externally the raised ribs are equal in width with the intervals between 

 them, and the concentric sculpture, while extending over ribs and 

 interspaces, is stronger in the intervals between the ribs. Ears 

 moderate, apparently not ribbed. The specimens vary considerably 

 in size; the one figured, a small specimen, measures: length 41 mm. 

 by height 36 mm. Others were much larger, attaining a length of 55 

 mm. or more. 



Named in honor of Dr. Christopher Nugent, the first to publish 

 an account of the geology of Antigua. Collected at Hodge's Bay. 

 Cotypes, A. N. S. P. Collection, invertebrate fossils, No. 1,656. 

 Ostrea antiguensis n. sp. Plate XIX, fig. 7; plate XX, figs, l, o, 6. 



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 upper 

 or flat valve has the margin strongly reflexed to fit the upturned 

 margin of the deep 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 turned-up margin. 0. haitensis 

 Sowb. has the rugose exterior of this species in its strongly plicate 



