224 DR W. A. HEKDMAN ON 



Polycarpa pusilla, n. sp. (Plate XXXV. figs. 4-6). 



External Appearance. — The body is spherical, ellipsoidal, ovate, or pyriform, 

 is not compressed, and is unattached. The anterior end is narrower if not the 

 same as the posterior, which is wide and rounded. When the shape is ellipsoidal, 

 the long axis is dorso-ventral. The apertures are not distant, on the anterior 

 end; in some cases prominent, in others sessile and inconspicuous; no lobes are 

 visible. 



The surface is even, but completely covered by an incrusting layer of fine 

 sand. Hair-like processes are present on the posterior half or so of the body, 

 and bear sand grains. 



The colour is light brown. 



Length of body (in an average sized specimen), 5 mm.; breadth, 6 mm.; 

 thickness, 4 mm. 



The test is moderately thick and tough, completely concealed externally by 

 the sand, and smooth internally, it is continued posteriorly into the hair-like 

 processes bearing sand grains. 



The mantle is rather strong. The muscle bands are numerous, though fine, 

 and form a close network. Most of them compose a strong longitudinal layer 

 internally, and a weaker circular layer externally. The sphincters are well 

 developed. 



The branchial sac has four folds upon each side. The internal longitudinal 

 bars are very broad, ribbon-like membranes: there are four or five on each fold, 

 and one or two in the interspace. The meshes are rather large and square, and 

 contain each five or six stigmata. In the mature sac the stigmata are long 

 and narrow, and each mesh is divided transversely by a narrow horizontal 

 membrane. 



The tentacles are of two sizes, with occasional smaller ones between. There 

 are usually upwards of fifty altogether in the circle. 



The dorsal lamina is a narrow membrane with slight transverse ribs, which 

 begin a short way from the anterior end. The edge is thickened, but has no 

 denticulations. 



The dorsal tubercle is simple, and ovate in outline; the aperture is directed 

 anteriorly and to the left. The horns are not coiled, but almost touch ; the long 

 axis is vertical. 



Locality. — Thirty-five specimens of this species were obtained 40 miles off 

 Valentia, at a depth of 110 fathoms in the North Atlantic ; and one specimen 

 was obtained at Station 31, " Porcupine " 1870, lat. 35° 56' N., long. 7° 6' W., 

 at a depth of 477 fathoms; bot. temp., 10 o, 3C. 



This is a curious little species, in external appearance bearing considerable 

 resemblance to Polycarpa pilella, a species discovered during the "Challenger" 

 Expedition at Bahia, in shallow water. The present species is usually spherical, 



