178 PERCY SLADEN TRUST EXPEDITION 



The course of the intestine from the buccal mass to the visceral nucleus is the usual 

 one (fig. l). The rather stout oesophagus gradually widens out into an elongate swelling, 

 which seems to act like a crop, in which food is preliminarily stored. Afterwards the 

 intestine becomes a slender thin-walled tube, entering finally into the visceral nucleus 

 (fig. 3, n). Here it is joined by the liver, enlarges into the stomach, and leaves the 

 visceral nucleus at the left side of the foremost portion of the last named organ, bends 

 over to the right side and forms an anus (fig. 1, a) beneath the thickened margin of the 

 mantle. 



The visceral nucleus, composed of the liver and the gonads, exhibits an elongated 

 shape (figs. 1 — 3), and is placed in the centre of the disc, in a broad, longitudinal groove 

 of the cutis ; at the posterior pole two spiral turns of the gonad, indicating the former 

 position of the shell, are visible, at least as seen from the right side (fig. 2). As has been 

 already mentioned the shell itself was not present in my specimen. According to Hedley's 

 statement*, it is much like a very depressed Carinaria shell, with a small spiral portion 

 of 2-| whorls, "at right angles to which extends the adult, boat-shaped shell, white, glassy, 

 shining, most brittle, ornamented by a double, lamellar keel, running from the embryonic 

 shell along its periphery ; from keel to margin curved growth lines undulate the side of 

 the shell." From this description it may be inferred that the shell is like that of 

 Carinaria, though, judging after the general shape of the visceral nucleus, one would 

 rather think that the shell must resemble that of Cardiapoda. 



The nucleus is enclosed within the very thin mantle, showing at its foremost part a 

 thickened margin (fig. 3, mr, fig. 1). Perpendicular to the longitudinal axis of the nucleus, 

 a parallel row of about eight tiny gills (fig. 3, g), of the same structure as in Cardiapoda, 

 extends downwards, accompanied at the left side of the base by a much elongated 

 osphradium (os). Dorsally to this is situated the heart (fig. 1, at, v), with the atrium 

 turned forward towards the gills, and receiving from them the aerated blood. On 

 examining the mantle from above, we may also, through its thin walls, detect the kidney 

 (Hg. I, k), lying proximally and close to the rectum, on the median line. Its structure is 

 likewise the same as in Cardiapoda, showing the same complicated structure of its walls. 

 I could not observe the opening to the exterior, nor the renopericardial passage. 



Finally we may note, at the right side of the base of the fin, the small penis (fig. 4, p). 

 As in all Heteropods, the copulating apparatus consists of two parts, (1) the penis properly 

 so called with a very deep seminal groove, and (2) distally from this a somewhat larger 

 accessory apparatus probably to ensure copulation, though I could not observe the 

 glandular structure, so distinct in Carinaria, the mucous secretion of which is ob- 

 viously a help in copulating. 



As to the place of Pterosoma in the system, we may safely say that it is nearly 

 related to Carinaria, as is indicated by the visceral nucleus and the shape of the shell, 

 also by the separate muscles in the fin. It occupies a position intermediate between 

 Carinaria and Cardiapoda, but is distinct from both genera by its broadly expanded body. 



Pterosoma planum was first found, about 90 years ago, by Lesson, between the 

 Moluccas and New Guinea, afterwards by Cuthbert Collingwood in the Channel of 

 Formosa, by Hedley near Sydney, by the Challenger t on the route between the 

 * I.e. p. 335, fig. 2. t Recorded by me, I.e. p. 23. 



