MUSEUM OF COMPARATIVE ZOOLOGY. 207 
valves. Other characters seem equally interchangeable, such as the armature 
of the lips, which may be internally striate or smooth, externally smooth, papil- 
lose, or arborescent. 
All these facts confirm me in my belief that the subdivisions of the group 
may advantageously be limited to a comparatively small number, 
Suscenus JANIRA ScHUMACHER. 
Pecten (Janira) hemicyclica RaveEnet. 
Janira hemicyclica Tuomey & Holmes, Miocene Fos. S. Car., p. 25, pl. viii. figs. 
1-4, 1855. 
Pecten hemicyclicus Ravenel, fide T. & H. 1. c. 
Plate VI. Fig. 5. 
Two lower valves of this species were dredged on the west coast of Florida 
by the Bache in 19 fathoms. It is found not very rarely on the east and west 
coasts of South Florida, and often identified as P. ziczac. The ribs on the flat 
valve differ greatly in different specimens, being sometimes obsolete and some- 
times very strong. The color of this valve is much as in P. ziczac. The color 
of the convex valve and its sculpture are quite different from those of P. ziczac, 
which grows to a considerably larger size at present. The fossil specimens 
of hemicyclica, as figured, are larger than any recent ones I have yet heard of. 
The very young of this species are externally indistinguishable from the fry of 
P. magellanicus Gmelin and Amusium plewronectes. The transverse rugosities 
or grooves of the hinge-line referred to in Pseudamusiwm thalassinum are well 
marked in the fry of this species, and very evident traces of them are visible 
in the adult. In the young they occupy a lanceolate area on each side of the 
cartilage pit, and are shown in the figure, considerably magnified, on Plate VI. 
These shells and some other young fry are not to be distinguished from young 
Pecten similis Laskey, of most collectors. I find fully half the “ P. similis” of 
the Jeffreys collection to be of this character. Many of them might have 
grown to be that species, but many probably might not. Unusual localities, 
such as Korea or Jamaica, quoted for P. similis (genuine) on the authority of 
Dr. Jeffreys, should be suspected or held for more information. 
Suscenus AMUSIUM (Botten) ScHuMACHER. 
Historical Synonymy. 
Amusium Rumphius, Amboinische Rariteitkamer, pp. 144, 188, pl. xlv. figs. A, B, 
1705. Klein, Tent. Meth. Ostrac., p. 184, 1753. Martini, Verzeichn. 
Samml. Nat., 1774. 
Synonymy Proper. 
Amusium Bolten, Mus. Boltenianum, ed. i. p. 165, 1798; Pecten pleuronectes auct. (no 
description or type mentioned). 
