MUSEUM OF COMPARATIVE ZOOLOGY. 239 
P. undatus and P. pilosus. The carolinensis form of Holmes is little cancel- 
lated, and grows very large ; 10 cm. is not an uncommon length. It is abun- 
dant in rather deep water as far north as Cape Hatteras, but not common 
inshore. In the Antilles the lineatus form is not uncommon, and averages 
smaller than the preceding. The strength of the radiating undulations is very 
variable ; they may be very evident, numerous, and even a little keeled in the 
middle, or flat, rounded, and strongest in the middle part of the valve, or alto- 
gether obsolete ; they are rarely discernible in cancellated specimens, but many 
which are not cancellated are entirely without them. 
Pectunculus pectinatus GMELIN. 
Pectunculus variegatus ? D’Orb., Bull. M. C. Z., TX. p. 118. 
Arca pectinata Gmel., S. N. 8818, 1790. 
Pectunculus pectinatus Lam., Hanley, Rec. Sh. p. 165. Reeve, Conch. Icon., fig. 28. 
Arca pectunculus minor Chemnitz, VII. t. 58, figs. 570, 571, 1784. 
2 Pectunculus oculatus Reeve, Conch. Icon., fig. 38, 1843. 
Pectunculus pectiniformis D’Orbigny, Moll. Cuba, p. 313 (? not of Lamarck). 
P. aratus Conrad, Tuomey & Holmes, Pliocene Fos., p. 50, pl. xvii. figs. 6 a, 6 b. 
P. charlestonensis Holmes, Post Pliocene Fos., p. 16, pl. iii. fig. 5, 1858. 
Habitat. Gulf of Mexico, west of Florida, 30 fms.; Charlotte Harbor, 
Florida, 13 fms.; off Sombrero in 54 fms.; Sigsbee, off Havana, 80-119 fms.; 
off Gordon Key in 68 fms.; Station 10, off Cuba, in 37 fms.; Station 32, Lat. 
23° 32/ and Lon, 85° 5’ W. Gr., in 95 fms.; Stations 36 and 45, off Cuba, in 
84 and 101 fms.; Station 56, in 175 fms., off Havana; Station 117, 874 fms. 
(one valve); and Station 278, in 69 fms., Barbados. 
Var. carmatus Dall, at Station 247, near Grenada, in 170 fms., ooze, bottom 
temperature 53.°5 F. (living), and at Barbados in 100 fms. 
The shell before us is with certainty the pectinatus of the best authorities ; 
one of its varieties seems to have been identified with the East Indian Arca 
pectunculus of Linné (Pectunculus pectiniformis Lam., not D’Orb.), which 
I have not found authenticated from the West Indies. It is probably the 
oculatus of Reeve, and certainly the aratus of Conrad. The different forms 
observed by me are three. 
The first one has fewer ribs (about 20-30), about sixteen plications of the 
basal margin inside ; very square channels between the ribs ; close set, elegant 
concentric wrinkles over the whole ; and in many specimens a (sexual?) pe- 
culiar truncation of the shell behind the hinge-line with a consequent angu- 
lation more or less pronounced ; the colors pink or rosy, or white with pinkish 
blotches, with dark pink or brown blotches, or, oftener, variegated tracery of 
lines. The above is most like the Linnean species, and is probably what has 
been so named. 
The second or typical form has the ribs either more numerous (30-40) or 
wider with shallow hardly channelled interspaces ; is whitish with brown 
