REPOET ON THE ANNELIDA. 
457 
pass to the inner surface of the circular coat, having internally (superiorly) only a basement- 
band, the thin stratum of longitudinal fibres, and the foliate glandular masses. The 
hypoderm outside the circular coat, again, is at once firmer and narrower. The oblique 
muscles are well formed and powerful, and are inserted at the outer borders of the wide 
median hiatus, which is about thrice the transverse diameter of the nerve-area. The 
longitudinal ventral muscles are firm, wedge-shaped masses bounded internally by 
the oblique, and externally by the circular muscular coat. The longitudinal dorsal 
form extended plates of nearl}^ uniform diameter, and separated superiorly by a rather 
wide hiatus. From the latter issues the broad suspensorial band of the alimentary canal. 
The latter is firm and finely striated from the closely arranged glands. The oesophageal 
region has an external investment, showing many longitudinal fibres, a thick circular 
muscular layer, and a symmetrically folded glandular lining. The glands on the edges 
of the opposing folds have such a disposition that they resemble ears of wheat. The 
perivisceral chamber also contains the ovaries with ova at various stages. 
Pista corrientis, n. sp. (PI. XLVIII. fig. 11 ; PI. XXVTIa. fig. 35). 
Habitat. — Amongst the tubes of Pista mirabilis was a fragment of a sandy tube, 
strengthened by Foraminifera, greenish translucent grains of chlorite, and other debris, 
containing the species above mentioned. It also, therefore, belongs to Station 320 (off 
the mouth of the Eio de la Plata), February 14, 1876 ; lat. 37° 17' S., long. 53° 52' W. ; 
depth, 600 fathoms ; bottom temperature 37°'2, surface temperature 67°'5 ; sea-bottom, 
oreen sand. 
O 
The form is comparatively small, measuring about 28 mm. in length, and having a 
diameter anteriorly of a little more than 1 mm. 
In comparing the anterior region with that of Pista cristata, the great development 
of the lateral lamellse of the second segment is conspicuous. These form large lobes on 
each side, projecting as far forward as the most anterior cephalic flap. The tentacles 
being absent, the head-lobe appears to be sheathed in them, when viewed from the 
ventral surface. A wide gap exists between their dorsal edges, and a smaller between 
their ventral, the lamellae arising more abruptly at the former than the latter. The 
lamellae of the third segment are, perhaps, somewhat larger and thinner tlian those of 
Pista cristata, but instead of being borne erect or carried forward, each is reflected 
backward, so as to cover a series of ocular specks, ranged in a dense row posteriorly at 
their base. The dorsal surfaces of this and the foregoing segments are large, and bear 
traces of the pedicles of four branchise, but nothing further can be said of the latter. 
The bristles possess comparatively short tips, with well-marked wings. They are 
proportionally shorter than in Pista cristata, while the winged region is longer and 
better developed. 
(ZOOL. CHALL. EXP. PART XXXIV. 1885.) 
LI 58 
