NO. 1264. ILLUSTRATIONS OF AMERICAN SHELLS— BALL. 507 
PECTEN (PLAGIOCTENIUM) GIBBUS var. AMPLICOSTATUS Dall. 
Plate XXXII, fig. 9. 
Pecicn gihbus var. amplicostatus Dall, Trans. Wagner Inst., Ill, Pt. 4, 1898, 
p. 747. 
Coast of Texas and south to Cartagena. U.S.N.M., 106990. 
One valve is usually white, the other of a slaty gray, more or less 
variegated with white and brown. 
LIMA (CTENOIDES) ALBICOMA Dall. 
Plate XXXII, fig. 2. 
Lima alhicoma Dall, Rep. Blake Pelec, Bull. Mus. Comp. ZooL, XII, No. 6, 
1886, p. 225. 
Off Habana in 115 fathoms, and at Barbados in 100 fathoms. 
U.S.N.M., 62250. 
The color of the shell is grayish white, or with a slight tinge of 
3'ellow. 
PHILOBRYA ATLANTICA Dall. 
Plate XXXII, figs. 4, 5. 
Philohrya atlantica Dall, Proc. U. S. Nat. Mus., XVIII, 1895, p. 16.— Bernard, 
Journ. de Conchyl., XLV, 1897, p. 10, pi. i, fig. 2, 
Spiring Bay, Argentine coast, attached to algae in 58 fathoms. 
U. S. Fish Commission steamer Albatross. U.S.N.M., 97057. 
Bernard, in discussing this species, has not quite clearly understood 
my meaning, when, in my original paper, 1 compared the nepionic 
valves of this species to a Naiad glochidium. I did not mean that the 
Pliilobrya passed through an encysted stage in its early development 
necessarily, or that the development of the soft parts before the post- 
nepionic development of the shell was necessarily equivalent to that 
of the naiades, but merely that the nepionic stages of the valves were 
comparable, which is undoubtedly the case, though the resemblance 
may be less close than I was at first disposed to believe. The shell is 
of a purplish color, with an olivaceous periostracum, fimbriated on 
the radial lines, and the young are retained within the maternal shell 
until of a considerable size, this period, perhaps, corresponding to 
the period of encystment in the naiades. 
CRENELLA PECTINULA Gould. 
Plate XXXI, fig. 11. 
Modiola jJeclinula Gould, Inv. Mass., 1841, p. 127, fig. 85. 
Modiolaria pectinula Gould, Otia, 1862, p. 182. 
Crenella pectimdu Stimpson, Checkl. East Am. Shells, p. 2, Smithsonian Misc. 
Coll., 1860. 
