A. E. Verrill — Marine Neinerteans of Nexc England^ etc. 441 



TIOUBTFUI. SPECIES. 



CerebratuluS medullatUS Hubrecht, Voyage of the Challenger, vol. xix, 

 pp. 39, 50, pi. xi, fig. 10 ; pi. xii, figs. 9, 10, 1818. 



PLATE XXXIX, FIGURE 17. 



Tliis species was described from a mere fragment, without head or 

 tail. It is said, however, to differ from other species in the structure 

 of the body-wall, which is thinner than usual. 



The inner glandular layer of the integument and the inner base- 

 ment membrane are wanting, as distinct layers, so that the outer 

 glandular layer and its basement layer are in contact with the outer- 

 longitudinal muscular layer. The median dorsal nerve, or nervous 

 thickening, is also unusually large and distinct, being from one- 

 third to one-fourth as thick as the core of the lateral nerve-trunks. 



Off Nova Scotia, in 85 fathoms. 



This species is probably not a Cerebratulus, as here defined, but 

 more likely belongs to Lineus or Micrura, and perhaps to some 

 of the speties described above. 



Suborder II, GYMNOCEPHALA. 



Holocephala Diesing, 1850, non Miill., 1835. 



Gymnocephnlidce, Kefferstein, Zeitsch. fiir wiss. Zoo!., xii, 1862. 



Ano'pla. (pars) Mcintosh, Nemerteans, p. 203. 



PalmonemfiTiini Hubi'echt ; Canis. 



Palceonemertea Hubrecht, Voy. Challenger, xix, p. 5, 1887. 



Palwomertina Lang, Text-Book of Comparative Anat., p. 178, 1891. 



Head without lateral slits, but sometimes having shallow trans- 

 verse or oblique fossae connected with small, ciliated (olfactory) 

 pouches or ducts leading to the posterior ganglions ; sometimes des- 

 titute of both fossiB and ciliated ducts. Mouth distinct, situated 

 back of the ganglions. 



Proboscis long and slender, more simple in structure than in the 

 Rhagadocephala. Usually only two (lateral) longitudinal blood 

 vessels are present. 



Ocelli often numerous, variously arranged, sometimes wanting. 



Lateral nerve trunks sometimes situated between the basal layer 

 of the cutis and the external circular muscular layer ; sometimes 

 outside of the longitudinal muscular layer; and sometimes in the 

 midst of the muscular layer of the body-wall ; usually connected 

 with a continuous nervous plexus. 



