226 DR W. A. HERDMAN ON 



Poly cm-pa curta, n. sp. (PI. XXXVI. figs. 7-11). 



External Appearance. — The body is ovate, ellipsoidal, or elongated trans- 

 versely; not compressed laterally, and unattached. The anterior end is wide 

 and convex, the posterior is usually still wider, and flat or irregular ; the dorsal 

 and ventral edges are short and similar. The apertures are rather far apart, 

 being placed at the opposite extremities of the anterior end. They are equally 

 anterior, and are sessile and inconspicuous. There are no apparent lobes. 



The surface is smooth, and fairly regular, but is slightly incrusted with 

 small sand grains. 



The colour varies from yellowish-grey to light brown. 



Greatest length of the body, dorso-ventrally (in an average specimen), 9 

 mm. ; breadth (antero-posteriorly), 7 mm. ; thickness, (laterally), 5 mm. 



The test is thin, but very tough and leathery. It is quite opaque. The 

 outer surface is slightly sandy, and the posterior end has a few hair-like pro- 

 longations, to which sand grains are attached. 



The mantle does not adhere to the test. The apertures are slightly cross- 

 slit, and the sphincters surrounding them are strong. The musculature else- 

 where on the mantle is well developed, the muscle bands forming a close net- 

 work not clearly divided into longitudinal and circular layers. 



The branchial sac has four well-marked folds on each side. The most dor- 

 sally placed is larger than the others, and has about twelve internal longitudinal 

 bars. Th e rest of the folds have about six bars each, and there are two bars 

 in each interspace. All the internal longitudinal bars are flat, ribbon-like 

 membranes of considerable width. The transverse vessels are all of the same 

 size. The meshes are about square, and contain each four or five stigmata. 



The dorsal lamina is a narrow membrane, with no ribs and no denticulations. 



The tentacles are not very numerous. There are eighteen or twenty large 

 tentacles, and the same number of smaller intermediate ones. 



The dorsal tubercle is simple. It is fusiform in outline, with the long axis 

 vertical. There is an irregular slit down the middle, but there is no curvature, 

 hence no horns are present. 



Locality. — Sixteen specimens of this species were dredged at Station 12; 

 " Lightning," 1868; lat. 59° 36' K, long. 7° 20' W.; depth, 530 fathoms ; bot. 

 temp., 6° -4 C. 



This species is allied to Polycarpa pusilla, but differs both in external appear- 

 ance and in internal structure. It is not so much incrusted with sand, and the 

 shape, though variable in both species, is here more decidedly elongated dorso- 

 ventrally (Plate XXXVI. figs. 7 and 8), the result being the apertures come to be 

 placed far apart at the opposite extremities of the wide anterior end (see Plate 

 X XXVI. fig. 7). The greatest length is always dorso-ventrally, and this ranges in 

 the specimens collected from 5 mm. to 13 mm. 



