PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 15 



symmetrical, covered with more elevated, crowded, concentric lamellae, 

 especially near the margiiis; liiugemargiu straight, or even a little 

 concave toward the umbo; peripheral margins of the valves strongly 

 and regularly crenulated and interlocking; interior regularly deeply 

 grooved, to correspond with the external ribs; lower valve slightly con- 

 vex, with about twenty-six regular even ribs, separated by channelled 

 interspaces somewhat narrower than the ribs ; the top surface of each 

 rib is flattened with abroad, shallow groove in the middle, with one or 

 two faint riblets on each side of the groove; the whole surface is cov- 

 ered with concentric lamellae, like those of the upper valve, but less 

 sharp, and about twice as crowded. Ears subequal, arched, covered 

 with crowded, elevated lamellae; byssal notch very small. Height of 

 shell, 90™™; breadth, 100™™ ; breadth of hinge-line, 34™™; thickness, 



1 rtmui 



This very elegant species, while also showing some general resem- 

 blance to P. eaurinus GId., forms a passage toward the section Janira, 

 and differs in many details from any described west-coast species, recent 

 or fossil, so far as figures and descriptions serve to indicate. 



Pecten Hemphillii, u. s. (7943). 



This species has a strong general resemblance to the last, and is best 

 described by comparison with it. P. HemphiUU is smaller, with sixteen 

 ribs, as against twenty-six in a P. Stearnsii of the same size, with which 

 throughout it will be compared; the lateral margins of the ears are 

 perpendicular and straight, instead of outwardly rounded ; the hinge- 

 line is perfectly straight, not slightly concave; the ribs on the lower 

 valve are flattened above, with symptoms of a groove on the top surface, 

 instead of beautifidly roundly vaulted ; the interspaces are of course 

 wider; the raised concentric lamellae toward the periphery become long, 

 coarse, and very crowded ; on the lower valve, the shell is more vaulted, 

 with hardly any traces of the raised lamellae, and with larger, rude, 

 hardly flattened, radiating ribs, which show no trace of grooving or 

 riblets ; the ears and byssal notch are smaller and more coarsely sculp- 

 tured. Height, 5G™™; breadth, 63™™; breadth of hinge-line, 28™™; 

 thickness, 15™™. 



This species seems to approach Janira even more closely than the 

 last, but the value of these sections of Pectinidw is very questionable. 



Anomia limatula, u. s. (7949). 



Shell large, thin, irregular, witn a rather thickened hinge-line; exter- 

 nal surface rough (when not worn), like the fresh fractured surface of a 

 piece of china-ware; a few faint radiating lines with the lines of growth 

 comprii^e the sculpture; shell originally yellowish, and still retaining 

 some of its color and lustre. Normal form apparently that of a Pecten 

 without ears. Breadth, 75™™; height, 70™™; arch of valve, 10-15™™. 



No lower valves were obtained. This large species is neither A. lampe 

 Gray no^; A. {Plac.) niacrosckisma Desh., which are the onl^^ recent spe- 



