1912.] NATURAL SCIENCES OF PHILADELPHIA. 513 



Pecten subhyalinus E. A. Smith, from the west coast of Pata- 

 gonia, is somewhat higher than long, the hinge line is shorter and 

 the valves somewhat less convex than in P. oligolepis. 



Pecten (Amusium) sol n. sp. PI. XXIV, figs. 1, 2. 



The shell is subcircular, thin, but slightly convex, nearly smooth 

 (the growth-lines being very faint) except near the beaks, where 

 there are radial riblets, low, rounded, but very distinct for a distance 

 of about 10-14 mm., then gradually becoming weak and disappear- 

 ing. In the left valve the beak is depressed, almost flat, and the 

 auricles are marked off by a small ledge, but no decided change 

 in the general curvature of the surface. In the right valve the beak 

 is somewhat convex and separated from the more distinctly de- 

 marked auricles by a groove. Internally the shell has radial ribs 

 in pairs, the interval between the ribs of a pair being about one- 

 third the width of the interval between pairs. 



Two valves, cotypes, measure 83 mm. from beaks to basal margin. 

 Some specimens represented by internal casts are larger, up to 

 90 mm. in altitude in the case of a large one. This valve measured 

 90 mm. in length. 



From a bed with Pecten oxygonum optimum in the Culebra Cut, 

 near Tower N, Las Cascades. 



This species and Pecten oxygonum optimum are characteristic 

 fossils of what we have called the Pecten bed, at Tower N. 



This Amusium differs from Pecten touloe, of the Gatun bed, P. 

 papyracea Gabb, of Santo Domingo, and the North American P. 

 mortoni by having strong radial sculpture in the early neanic stage: 

 those species agreeing with the recent Oriental forms in having no 

 external radial sculpture at any stage. P. lyonii Gabb, described 

 from Sapote, Costa Rica, agrees with P. sol in having radial beak 

 sculpture, but it differs by having more distinctly defined auricles 

 and by the internal sculpture of numerous equidistant ribs. While 

 the ribs of one valve are not perceptibly twinned in the Oriental 

 Amusiums, they are about equal in number in the two valves in P. 

 pleuronectes L., in which this character of having one valve with 

 equally spaced ribs and one with paired ribs is very pronounced. 

 With the single exception noted below, all of the casts we have seen 

 from the Pecten bed agree in having ribs in contiguous pairs. 



In one incomplete cast the ribs are in pairs separated by intervals 

 fully half as wide as the spaces between pairs (not crowded as in 

 P. lyonii Gabb). This probably represents another species. 



