138 Mr. P. S. Abraham on some Genera 



spirit specimens, is a uniform light brownish, the tint 

 becoming darker on the pallial expansion, on the dorsal ten- 

 tacles, the branchiae, and on the foot. 



Dimensions (in spirit) — length 100 millims., breadth 82, 

 thickness 21. 



Hah. The Red Sea. 



Two other species of Hexahranchus have been found in the 

 Red Sea, H. prcetextus and H. sanguineus. Irrespective of 

 coloration and markings, the former differs from H. suezensts 

 in having a more elongate outline, in being more depressed, 

 in having no interval underneath between the foot and the 

 mantle, and in having slenderer dorsal tentacles ; the latter, 

 in the shape of the tentacles, and in the larger, more slender, 

 and less dendritic branchias. 



Plocamopherus, Riippell & Leuckart. 



Body limaciform. Mantle represented by a supracapital 

 veil, bearing tuberculate or branched appendages on the 

 margin, and by two or three tubercular processes upon each 

 side of the back. Dorsal tentacles laminate and retractile. 

 Branchise few, plumose, non-retractile, anteriorly surrounding 

 the anus. 1'he tail bears dorsally a wavy crest. Mouth with 

 flat oral tentacles ; odontojihore with the spines near the 

 middle bicuspid, but none median : an incomplete buccal 

 collar. 



The genus " PlocamopJienis " was instituted by Riippell 

 and Leuckart* in 1828 for the reception of P. ocellaius, a mol- 

 lusk from the Red Sea. The generic name was misquoted 

 by Cuvier f as Phcamoceros ] and this word was afterwards 

 adopted by D'Orbigny and others. It has, however, been 

 generally written Plocamophorus. In the ' Proceedings of the 

 Zoological Society' for 1861, Mr. Pease has enunciated a 

 supposed new genus " HistiopJiorus^'' which, from his descrip- 

 tion, would appear to have the same characters as Plocamo- 

 pherus. 



The species hitherto described are : — 



P. ocellatuSj Riipp. & Leuck. loc. cit. 



P. ceylonicus, Kelaart (sp.) and Aid. & Hanc. in Trans. 

 Zool. Soc. vol. V. p. K:53, pi. xxxii. f. 4-6. 



P. imjyertalis, Angas, in Journal de Conchy liologie, vol. xii. 



P. maculatusj Pease (sp.), loc. cit. 



* Atlas Ton E. Riippell, ' Neue wirbellose Thiere des rothen Meers,' 

 p. 17,T.v. f. 3. 

 t " Regne Animal ' (nouvelle Edition, 1830), torn. iii. p. 62. 



