REPORT ON THE ANNELIDA. 
403 
often absent in the sections (from imperfect preservation). The circular muscular coat is 
fairly formed, and a thin basement-layer occurs between it and the hypoderm. The 
fibres of the circular ring do not form so evident an inner boundary to the nerve-area as 
usual, and the latter passes inward between the ventral muscles. A large neural canal is 
also present (PI. XXXVIIa. fig. 8). The longitudinal muscular layers are well defined, 
the ventral forming two elongated masses, bulky interiorly and tapering superiorly, and 
occupying double the circumferential extent of the dorsal. The latter in section form 
two elliptical muscles on each side of the median line, and constitute the dorsal arch. 
The oblique muscles are inserted over the outer border of the nerve-area. The 
alimentary canal has circular and longitudinal fibres externally and a frilled epithelial 
coat of considerable thickness internally. Toward the thin upper region of each 
longitudinal ventral muscle is an ovoid sheath filled with minute spherical bodies with a 
nucleus, which are probably the reproductive organs. 
This form somewhat approaches the Praxilla collaris of Claparede,’ from Naples. 
Praxilla lankesteri'^ n. sp. (PI. XXVa. fig. 3). 
Habitat . — A form that at first sight can hardly be distinguished from the foregoing 
was dredged at Station 232 (south of Yedo, Japan), May 12, 1875 ; hit. 35° 11' N., 
long. 139° 28' E.; depth, 345 fathoms ; bottom temperature 41°T, surface tempera- 
ture 64° '2 ; sea-bottom, green mud. 
The cephalic plate agrees generally with Praxilla kbllikeri, but there are no crenations 
on the dorsal margin, though it is notched in the middle line. There are also three 
segments provided with the simple inferior spine, and a collar at the anterior margin of 
the fifth segment as in the foregoing. 
The hooks, however, show a slight divergence (PL XXVa. fig. 3), for the fascicle of 
bristles is attached close to the base of the chief fang inferiorly, whereas an interval 
occurs in the former example. Moreover, the crown is less elevated, and the teeth less 
numerous, about five, as a rule, being visible in profile above the great fang. 
The somewhat coarse sandy mud in the alimentary canal of this form abounded in 
Diatoms, sponge-spicules, and other organisms. 
While in external configuration there is a close similarity between this and the 
foregoing species, there is considerable divergence on section of the body-wall. Thus the 
hypoderm in the present species is thick, and the circular muscular coat is firm and well 
defined, — keeping the semicircular nerve-area quite outside its continuous ventral region. 
No neural canal is visible. The longitudinal ventral muscles form a compact and some- 
what rhomboidal mass on each side, and do not occupy so large a part of the circurntt-rence. 
1 Aniiel. Chetop., p. 454, pi. xxvi. fig. 2. 
2 After Prof. Ray Lankester, who has paid much attention to the Annelida. 
