4 
G. STEWARDSON BRADY. 
Philomedes orbicularis. 
(Plate I., figs. 1-15.) 
Shell of the female seen from the side almost circular, except in the region of 
the sinus at the ventral margin, length about one-fourth greater than the height 
(fig. 1) ; anterior extremity obtusely angulated above the rostrum, posterior broadly 
and evenly rounded, dorsal margin rather boldly arched throughout its whole length, 
ventral strongly arched from the deep subrostral sinus backwards. Seen from 
above (fig. 2) the outline is broadly ovate, rounded behind and submucronate in 
front, greatest width situated in the middle and equal to about two-thirds of the 
length. Surface of the shell smooth and densely clothed with a villous coating of 
very short hairs ; margins of the rostrum and subjacent sinus fringed with stiff 
setse (fig. 6). Shell of the male (fig. 3) somewhat elongated, height not greatly 
exceeding one-half of the length, rostrum and sinus less developed than in the 
female ; posterior extremity obliquely subtruncate, slightly sinuated in the middle 
and rounded off ventrally ; dorsal margin well arched, ventral forming a continuous 
flattened curve. In the young condition (figs. 4, 5), the shell of the female in 
lateral view has the postero ventral angle sharply produced and is mucronate when 
seen dorsally. The soft parts of the animal have the typical characters of the 
genus, but the antennal setae (fig. 8) form two distinct series, the distal set being 
about twice as long as the proximal; the secondary branch of the female antenna 
(fig. 9) is two-jointed, the basal joint bearing a few short marginal setae, the 
second joint four marginal setae, one of which is longer than the rest and plumose, 
also a single lash-like apical seta. The secondary branch of the male antenna 
(fig. 10) is much like that of P. brencla, but less robust and its marginal setae are 
shorter. The principal tooth of the second maxilla (figs. 12, 13) is very large and 
strong, somewhat hatchet-shaped, the two extremities produced into strong cutting 
lobes, with a third smaller lateral tooth—the appearance of the whole organ, 
however, varying very much according to the position in which it is seen. The 
other limbs present no features calling for special remark. Length, 2 • 5 mm. 
P. orbicularis was found only in two gatherings (May 23, 1902 and June 15, 
1902). It is in all respects very similar to the well-known European species 
P. brenda and may perhaps be fairly looked upon as a southern variation of that 
form. There is the same characteristic villous covering and the size is nearly the 
same, but there is a total absence, in the adult, of any posterior angulations of the 
shell, which is also considerably more tumid than that of the northern species. 
The rather well marked constriction of the anterior, and the broadly rounded 
character of the posterior extremity, when seen dorsally, are also noteworthy features. 
The form of the shell in P. brenda seems to be the same throughout life : at any 
rate the smallest specimens I have seen present characters exactly the same as those 
