182 PERCY SLADEN TRUST EXPEDITION 



tubercles, neither are there spines before the eyes. At the left side of the very slender 

 visceral nucleus three or four minute gills are present. 



The middle plate of the radula, investigated by me in the only intact specimen, 

 exhibits a short, broad central cusp, at either side of which extends a row of four or 

 five smaller ones. The palatinal teeth number four in each row. 



17. Pterotrachea (s.s.) scutata (Gegenbaur). (Plate 14, figs. 1 — 3.) 



Stat. 1 (1), Nazareth Bank. Dredging station D 5 (l), Providence. Two specimens, 

 both females, were caught, with a total length of 52 and 76 mm. respectively. 



The most remarkable character of this species is the considerable development of the 

 cutis on the proximal half of the body (figs. 1, 2). It is true that in all intact specimens 

 of Pterotrachea, if rightly preserved, the cutis on the first part of the body, especially at 

 the ventral side, is somewhat thickened, leaving a kind of gular groove ventrally ; here, 

 in Pt. scutata however this character is much more accentuated. Seen from above (fig. 2) 

 the body is much broadened out at its proximal half by the thick cutis, exhibiting at the 

 ventral side a rather deep groove, into which the proboscis can be bent back. The whole 

 cutis is perfectly transparent, and of a tough, semi-cartilaginous nature, as in Pterosoma. 

 Also in other respects a comparison with this genus may be allowed as in Pt. scutata the 

 foremost margin of the cutis projects beyond the eyes and forrns a slight emargination. 

 Distally the thick envelopment of the body is soon reduced, though it remains very tough. 

 Everywhere spines and tubercles are found, especially on the dorsal side, where some 

 indistinct longitudinal rows are formed (fig. 2), at either side of the gular groove, in the 

 region of the visceral nucleus (which is surrounded, proximally and distally, by two longi- 

 tudinal, minutely toothed crests), and on the tail where the lateral rows follow exactly the 

 second and third muscular bands. There are no spinules on the proboscis nor any denticles 

 in front of the eyes, except those on the anterior margin of the thickened cutis. 



The pi^oboscis is rather weak, measuring only ^ of the total length of the animal. 

 The rounded fin, without sucker in my female specimens, is situated half-way between the 

 eyes and the visceral nucleus (fig. 1) and is very small. The visceral nucleus is elongated, 

 slender, with about eight gills at its front and left side. The tail ends in a pair of 

 horizontal, unusually tiny fins. 



I have no doubt this species is the same as that described by Gegenbaur*, who 

 particularly emphasizes the existence of the thickened cutis between the eyes and the 

 region of the fin, in the following words: " der Vorderteil ist...durch eine betrachtliche, 

 vorziiglich nach der Seite hin ausgedehnte Masse der glashellen Bindesubstanz aus- 

 gezeichnet, und unterscheidet somit diese Art leicht von den iibrigen bekannten Arten. 

 Diese Ausbreitung der Leibeshulle beginnt vorn an der Basis der Riissels, setzt sich in 

 sanfter Wolbung...iiber den Anfangsteil des Ruckens fort, schlagt sich an beiden Seiten 

 in Form starker Wlilste nach unten und begrenzt dort eine vorn schmale und tief nach 

 hinten zu sich erweiternd auslaufende Grube, in welche der Paissel sich teilweise einlagern 

 kann. Gegen die iibrige Korperoberflache ist diese kapuzenartige Wulstung tiberall scharf 

 abgesetzt." 



* Untersuchungen iiber Pteropoden und Heteropoden, p. 185, PL vm. figs. 19, 20, 1855. 



