138 DR A. MILNES MARSHALL ON THE 



siderable numbers at a depth of about 40 fathoms, and of sizes varying from 

 20 mm. long, with only a single polyp, to 125 mm. long, with 24 polyps. 



A single specimen was obtained by Panceri from the Bay of Naples,* and 

 during the " Porcupine " expedition two specimens were obtained by Carpenter 

 and Wyville Thomson t off the N.W. coast of Scotland, — one in 59° 41' N., 

 and 70° 34' W., at a depth of 458 fathoms, the other in 59° 34' N., and 7° 18' 

 W., and at 542 fathoms depth. 



External Characters. — The " Triton " specimens vary much in size, and in 

 the number and arrangement of the polyps. The smallest specimen is 26 mm. 

 long, and has only two polyps ; the largest specimen in the collection, the 

 single specimen obtained by the " Knight Errant," is 88 mm. long, and bears 

 18 polyps. 



The general appearance of one of the average specimens of the " Triton " 

 collection is well shown in PL XXIV. fig. 23 ; the specimen being drawn from 

 the dorsal surface, double the natural size. 



The rachis, which is somewhat club-shaped, is widest a short distance below 

 its upper end, from which point it tapers upwards to a blunt point. It bears 

 on its dorsal and lateral surfaces the polyps, which are few in number, and of 

 large size. Between the polyps the surface of the rachis is studded on all 

 sides with zooids, excepting a short tract immediately below each of the 

 polyps, which is destitute of zooids. 



The stalk (fig. 23, b), which forms rather more than half the entire length of 

 the colony, and which is distinguished from the rachis by bearing no zooids, 

 is oval in section, as shown in fig. 27, and of tolerably uniform size along its 

 whole length, except at its lower end, which presents a terminal thin- walled 

 dilatation. 



The arrangement of the polyps differs a good deal in different specimens, and 

 it is difficult to make out any definite system. In all cases the uppermost 

 polyps, those nearest the top of the rachis, are the largest, and the lowest ones 

 the smallest. The most usual arrangement is that shown in fig. 23. Here 

 there are six fully developed polyps arranged in two sets, an upper and a lower 

 one, each of three polyps. Of these three, one is inserted in the dorsal surface 

 of the rachis very close to the mid-dorsal line, or actually in it, while the other 

 two are inserted on the sides of the rachis a little way below the dorsal polyp, 

 and not quite opposite one another, the right hand polyp being as a rule a little 

 above the left hand one. The three polyps of each set are of about equal size, 

 but those of the upper set are much larger than those of the lower set. Below 

 the lower set can be seen in many specimens, as in the one figured, a third set of 



* Panceri, " Intorno a due Pennatularii l'uno non per anco trovato nel Mediterraneo, l'altro 

 nuovo del nostra golfo," Rendiconto ddV Accidentia delle scienze fisiche e matematiche, Napoli, 

 Giugno, 1871. 



t f Vide Kolliker, op. cit., p. 306. 



