4 G. STEWAEDSON 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 

 setae (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 setse, the 

 second joint four marginal setse, 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. brenda, but less robust and its marginal setse 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. Itrenda 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. brvnda seems to be the same throughout life : at any 

 rate the smallest specimens I have seen present characters exactly the same as those 



