442 " THETIS " SCIENTIFIC RESULTS. 



tance xip the visceral coil on the right of the nephridium. 

 The walls bear numerous large glandular swellings. "J'he orifice 

 is situated well forward on a level with the anus. 



The characters which have been seen in both species are : — The 

 external features generally and the organs of the pallial complex, 

 the proboscideal complex, the alimentary canal (except the 

 anterior portion of the oesophageal loop), the ribbon-like posterior 

 prolongation of the oesophageal gland, the hepato-pancreas and the 

 first hepato-pancreatic duct, the external appearance of the nephri- 

 dium and the pores of the nephridial gland, the pericardium, 

 heart and cephalic artery, and finally the uterus and ovary. 



The most important points of difference are : — The presence in 

 one and absence from the other of a ureter, the degree of develop- 

 ment of the hypobranchial mucous gland, and the form of the 

 individual teeth on the radula. 



With these two exceptions all the organs observed in both 

 species are essentially similar. 



The most important omissions from the account are : — The 

 visceral ganglia and visceral commissure, the otocysts and otocyst 

 nerves, and the oviduct. 



v.— COMPARATIVE. 



The 'protoconchs of the two species are (p. 4-38) stated to be of the 

 one type, which is there termed the Perostylus protoconch. 

 The name is adopted from Pilsbry's-'' two papers on the larval 

 shell of M. araanux. It must, of course, be admitted that they 

 are rather extremes of this type, which may be defined as: — 

 A turretiform protoconch, having whorls not increasing, or 

 increasing very slightly in diameter, and having a comparatively 

 large nucleus. Besides the two apices here discussed, those of 

 the following are also referable to thistyj)e: — Fusus hexagoncdis, 

 Tate,^ T'urbinella i-eyina, Heilprin, J and perhaps also that of 

 Chrysodovius contraria, Liun.,§ but the figure of this is poor and 

 the protoconch itself has not been seen by the writer. 



A glance at the figures referred to and those on pp. 421 and 431 

 accomjDanying this paper will show that these apices may reason- 

 ably be grouped together, and that the most important differences 

 between them lie in the number of whorls. This fact may be 

 further demonstrated by covering up so much of the figures that 

 all shall appear with the same number of whorls. 



* Pilsbry— 77ie Nuutilm, viii., 1894, pp. 17 and 67. 



+ Harris— Brit. Mus. Cat. Tert. Moll, L, Australasia, 1897, p. 131, pi. v., 

 f. 5. 



X Dall— Tert. Moll. Florida, (Trans. Wagner Free Inst. Sci.), iii., 1, 1890, 

 p. 98, pi. iii., f. 4. 



§ Baker— Ann. N.Y. Acad. Sci., ix., 1S97, p. 694, fig. 3.3. 



