336 MAIACOZOA. TROPIOrODA. NUDIBEANCHIATA* 



anteriorly with a tliick, narrow, crenulated margin, 

 nearly encircling the month. Two obtnse tentacula, 

 retractile into tubular sheaths. The mouth in the form 

 of a very large subglobose, somewhat compressed mass, 

 of greater diameter than the body, with a thick margin, 

 forming a vertical slit, and furnished with two very large, 

 convex, thin teeth, with semicircular margins ; its floor 

 divergently striato-sulcate, with a medial groove. Bran- 

 chial prominences gelatinous, caducous, ramose, distant, 

 arranged along the sides in a single series, in sinuses 

 formed by the dorsal margins ; orifices of the intestine 

 and genital organs separated. 



The genus diiters from Tritonia in the form of the 

 mouth, the separation of the lateral orifices, and the 

 compression of the body. It differs equally from Meli- 

 boea, and all the other genera, of which I have seen 

 descriptions. '2(^aipa, a globe ; o-roiia, mouth. 



1. Sjihcerostoma Jamesonii. Jameso7i^s Sphcerostoma. 

 Body oblong, much compressed, tapering behind to a 

 rounded point. The foot linear-oblorig, extending along the 

 entire length of the body, antenorly abrupt, narrowed and 

 rounded behind, with the surface rugose, and the margins un- 

 dulated. The sides erect, fiat, smooth, at the middle higher 

 than the breadth of the foot. The upper part or back arched 

 in both directions, little broader than the foot, covered with 

 soft, unequal, granulated, convex prominences ; the margin 

 slightly projecting beyond the sides ; the anterior margin thick, 

 narrow, rugoso-granulate, extending over two-thirds of the 

 kind of neck that supports the mouth. Immediately behind it 

 are two short tubes or sheaths, having a rather firm circular 

 margin, and in each is a conico-convex gelatinous darkish-grey 

 tentaculum. Terminating the body anteriorly is a large, sub- 

 globose mass, of cartilaginous consistence, and yellowish-white 

 colour. It is attached by a very short neck, and has the sur- 

 face longitudinally and transversely striato-rugulose. An- 

 teriorly it presents an oblong vertical slit, or mouth, having 

 the margin thick and rounded ; within which are seen two 

 large horny, brownish-yellow teeth, one on each side, exter- 

 nally convex, with a thin semicircular margin. These teeth 

 meet above and beneath. The floor of the mouth is formed of 

 a soft, white, convex mass, having a medial groove, and 



