NOTOMASTUS. 275 



sections of Notomastus latericeus in which the large genital funnels open to the exterior), 

 and are quite independent of the segmental organs. 



The GapitellidcB occur in sand or mud, in fissures of rocks, or in tubes amongst 

 littoral alga3. Their food consists of minute organic fragments of various kinds in sandy 

 mud, besides Foraminifera, Radiolaria, and Diatoms. The anterior region is often of a 

 bright red as in Notomastus. One of the most remarkable is the genus Scfphoproctus, 

 recently described by Gravier, 1 in which the posterior end terminates in a bristled scoop. 

 Their distribution is cosmopolitan, the common forms and Dasybranchus frequenting the 

 shore or shallow water, whilst some of the rarer forms range to 1340 fathoms in the 

 collections of the ' Challenger. 5 



Pelagic larvae appear in the tow-nets in July and are frequent in August, and at the 

 end of October such have the form shown in Plate XOIII, fig. 10. This is a minute form, 

 procured over a sandy bottom. The snout is pointed and rather conical, capable of being 

 withdrawn within the ciliated collar behind. Eyes two, brownish-black. Body more or 

 less cylindrical, slightly dilated in the middle, and again narrowed in front of the posterior 

 ciliated ring, the pygidial region being bowl-shaped, with the wide margin in front. The 

 alimentary canal shows a mouth but its lips do not project much. Within is an ovoid or 

 slightly elliptical pharyngeal region ventrally, the large globules of the yolk passing 

 dorsally above it. These globules are continued over the rest of the canal to the posterior 

 end, and in the pygidium are deep purple by transmitted light, a paler tinge extending 

 forward over the canal in the body. On each side is a close series of simple bristles. 

 The foregoing larva resembles that described and figured by Claparede and Mecznikow 

 as pertaining to Gapitella capitata, except that their larva was yellowish. It also differs 

 in coloration from that mentioned by Leschke, so that it may belong to another species, 

 e.g. Notomastus latericeus. 



Genus CXI. — Notomastus, Sars, 1851. 



Gapitella, Keferstein and Claparede; Arenia, De Quatref ages ; Sandanis, Kinberg. 



Capitellids, in which the anterior region is composed of twelve segments with two 

 rings, and eleven bearing capillary bristles. Head bluntly conical, with or without eyes, 

 with nerves from the anterior ganglia, and with ciliated nuchal organs between the 

 head and the peristomium with nerves from the posterior ganglion (Eisig). Two pairs 

 of cephalic ganglia. Peristomial segment broader than the succeeding. Anterior part 

 of the body sub-cylindrical. Feet with two fasciculi of capillary bristles; no mamilla. 

 The second region has its segments also two-ringed and furnished with ridges for hooks 

 dorsally and ventrally. In the first eight to thirteen segments of this (posterior) region 

 the two dorsal ridges of the foot coalesce into a single process in the dorsal median line. 

 Branchia3 none : only simple lobes of the feet, either dorsal or ventral. Side organs from 

 the first to the last bristle-bearing segment. Cup-organs occur on the proboscis, head, and 

 anterior region. The oesophagus seldom has a diverticulum. The ventral nerve-cord is 

 coelomic, with a large neural canal. The segmental organs occur in each of the posterior 

 segments. Reproductive products developed on the genital plate. The twelfth body- 



1 ( Nouv. Arch. Museum/ Paris, 4 e ser., t. viii, p. 181, pi. hi, figs. 200—204, 1906. 



