1911.] NATURAL SCIENCES OF PHILADELPHIA. 365 



ellae across the furrows on the ribs. They have been compared with 

 the types of the species by Dr. W. H. Dall. Fig. 2 measures, alt. 27, 

 width 27.8 mm. 



Pecten gatunensis Toula. 



Pecten (FlabeUipecten) gatunensis Toula, Jahrb., p. 711, PI. 26, fig. 2. 

 The fragmentary specimens taken add nothing to Toula's account. 



Pecten (Plagioctenium) operculariformis Toula. 



Pecten (JEqui'pectenT) operculariformis Toula, Jahrb., p. 712, PI. 26, fig. 3. 

 The ribs are narrower and have steeper slopes than in the related 

 recent P. nucleus. P. excentricus Gabb is a closely related, yet appar- 

 ently distinct form, from Santo Domingo. 



*Pecten levicostatus Toula. 



Pecten levicostatus Toula, Jahrb., p. 713, PI. 26, figs. 4 (5, 6). 

 Pecten thetidis Sowb. and Janira soror Gabb have been identified by 

 Gabb from Gatun (Journ, A. N. S. Phila., VIII, 346, 347). 



*Pecten (Amusium) lyonii Gabb. 



Pleuronectia lyonii Gabb, Journ. A. N. S. Phila., VIII, p. 347 (Gatun speci- 

 mens). 

 Pecten (Amusium) cf. mortoni Rarenel, Toula, Jahrb., p. 714, PI. 26, figs. 8, 9. 



This form is not present in our material. Gabb reported it from 

 Gatun, and Toula has figured specimens which have the appearance 

 of the Costa Rican species, the types of which are before us. 



Pecten (Amusium) toulae n. sp. PI. XXVIII, fig. 7. 



Pecten (Amusium) gatunensis Toula, Jahrb., p. 716, PI. 26, fig. 10. Not 

 Pecten gatunensis Toula, t. c, p. 711. 



The shell is smooth, thin and flat, equilateral, closely resembling 

 P. lyonii Gabb, of Sapote, Costa Rica (probably Miocene), and P. 

 papyracea Gabb. of the Santo Domingan Oligocene. The surface is 

 marked with narrow, sharply defined gray* rays on a white ground, 

 the rays less than half as wide as the intervals, subequal in the median 

 part, much narrower at the sides, where they gradually fade out, and 

 about 17 in number. Ears broad, subequal, marked with close, fine 

 growth-lines, more distinct than on the disk. Interior smooth, so 

 far as seen, but the marginal region, where ribs are developed in 

 related forms, is wanting in the specimen. Greatest breadth of the 

 broken specimen figured 48 mm. It attains a much greater size. 



In P. lyonii the gray rays are wider, when visible, and the spaces 

 between them are slightly convex; the interior has coarse radial ribs, 

 but none are visible in P. toulce where the inside is exposed, at the 

 lower margin of the broken shell. P. papyracea has fine internal ribs 

 in pairs. 



