40 OPISTHOBRANCHIATA OF BRAZIL 



Shell The shell (PI. X, fig. 40), is very thin and mem- 

 branaceous, the calcareous portion, small in amount, having been 

 broken and detached, was nearly all in small fragments in the 

 shell cavity. The outline of the intact membranaceous portion 

 is elliptical, with a moderate posterior sinus, as described by 

 Dall and Simpson. In length it measures 14.7 mm. and in maxi- 

 mum width 9.8 mm., though the membranaceous condition renders 

 the actual curvature a matter of some doubt. 



Pallial cavity. The pallial cavity is roomy, the branchial 

 plume, of the usual Tethys type, is nearly semicircular in out- 

 line, and extends transversely beneath the shell, its left margin 

 reaching well to the left side, the right tip projecting slightly 

 from beneath the mantle margin. 



Anal and renal opening. The anal opening is pocket like, 

 and situated upon the rear wall of the siphon tube, near its base. 

 In front of it lies the small inconspicuous renal opening near 

 the base of the branchia. 



Hypobranchial gland. The external opening of the Organ 

 of Bohadsch, or hypobranchial gland, lies upon the summit of a 

 low thickened elevation, just below the anterior end of the base 

 of the branchia, and 2.0 mm. distant from it. Upon the ventral 

 surface of the anterior end of the base of the branchia is situated 

 the osphradium, in the form of an oval yellowish depression. 

 Through the transparent body wall of this region many of the 

 nerves from the parieto-visceral ganglion complex may be traced 

 for varying distances. 



Reproductive openings. The genital opening lies just in 

 front of the anterior edge of the mantle, and is marked by an 

 increased pigmentation which is carried backward along the body 

 wall toward the opening of the Organ of Bohadsch. The female 

 portion of the opening is oblique and slitlike, the portion lying 

 above it is prolonged forward as a deep conspicuous groove 

 along the side of the body and head to the opening of the penis, 

 close to the right anterior tentacle, upon the side of the head. 



Tentacles. The anterior tentacles are strongly contracted, 

 broadly auriform, with a well developed external groove. Their 

 contracted condition precluded any even approximate measure- 

 ments. The posterior tentacles, or rhinophores, are also strongly 

 contracted, extending but 1.5 mm. above the surrounding sur- 



