MUSEUM OF COMPARATIVE ZOOLOGY. Zot 
slender, and composed of a central more solid rod with a tube on each side of 
it, and with its distal end enlarged in a somewhat hoof-shaped manner. From 
the blood-vessel in the base a single tube issues to the root of each rod and 
after continuing a short distance divides, one branch passing down one side 
of the rod, the other crossing to the opposite side and continuing to join the 
first again at the distal extremity ; it appeared as if the fluid passed down on 
one side and back by the other. The exterior of the filaments is abundantly 
ciliated, and though there is no organic connection, there is something in the 
character of the surface of the knobs at the ends of the filaments which makes 
them adhere tenaciously to each other or to any other part of the gill they 
may touch; I could see nothing peculiar, but the mechanical effect showed 
that something was there to produce it. The longest separate filaments were 
5.0 mm, in length, the diameter of the stalk of the rods measured about 0.025, 
and the knobs at the end 0.050 to 0.075 mm. The general outline of the gill, 
as traced by the terminations of the filaments, differs in different individuals 
to some extent. 
Habitat. Station 231 of Bartlett, in 1878-79, 95 fms., coarse sand and rock, 
off St. Vincent, bottom temperature 61°.5 F. Specimens on dead sea-urchin, 
tests and on the thin marginal expansion of the shell of Phorus; Barbados, in 
73 fms., coarse coral sand and broken shells, bottom temperature 70°.7 F.; 
Station 134, off Frederikstadt, Santa Cruz, in 248 fms., coarse sand and broken 
shells, bottom temperature 54°.5 F.; and Station 238, off the Grenadines, in 
127 fms., fine coral sand, bottom temperature 56°.0 F. A fresh valve was 
dredged by the U.S. Fish Commission, 36 miles S.4 W. of Cape Hatteras 
(Station 2601), in 107 fms., bottom temperature 64°.4 F. It will be seen from 
the above figures that the species inhabits the warmer area. 
The form argentea above described appears closely similar to the figures of 
D. Deshayesiana, given by Rouault. So nearly identical are they, that, until 
I have had an opportunity of comparing the recent and fossil forms, I feel 
barely justified in separating them. The figure of Ostrea tenuiplicata of 
Seguenza * resembled Dimya so much in its exterior that I requested Pro- 
fessor Seguenza to examine the interior and inform me of the character of the 
muscular impressions. He did so, and also most kindly sent me two valves 
which determine the correctness of my suspicions. The shell is an undoubted 
Dimya. It differs from Rouault’s figures and from the recent argentea in 
having a much stronger and coarser sculpture of divaricating radii, in its 
shorter hinge-line and proportionally larger cartilage pit ; the visceral area is 
smooth or slightly dotted, while in the recent form it is striated ; the relative 
position of the muscular impressions and their form also differ somewhat in 
the two shells. For these reasons, unless a considerable individual variation 
may be hereafter demonstrated, it would seem that the two species may be 
regarded as distinct. 
* Form. Terz. n. prov. Reggio, p. 128, t. xii. figs. 1, 1a, 16, 1880. Miocene, 
Aquitaniano, to Pliocene, Astiano, Calabria. 
