222 MARTIN ¥. WOODWARD. 



The Mantle. — In the contracted state of the dead animal 

 the mantle-slit, so characteristic of this genus, is inconspi- 

 cuous, and appears more like a broad, shallow sinus than a 

 deep narrow slit ; even in the living animal Mitsukuri was un- 

 able to observe its relation to the shell-slit. Its true relation 

 is, however, well seen in Dall's figures of P. Quoyana and 

 P. Adansoniana taken from the living animal. In these 

 forms we see that the margins of the mantle-cleft are closely 

 applied to the margins of the shell-slit, through which they 

 may slightly protrude. The free edge of the mantle is thick- 

 ened and closely beset with numerous small papillas, which 

 are evidently slightly protrusible, although not to the extent 

 seen in Haliotis. The mantle-fold completely encircles the 

 body, but is only feebly developed behind, and in this region 

 its margin is quite smooth. 



The Pallial Complex. — Owing to the bad state of 

 preservation of the specimens collected by the " Blake," 

 Dall was unable to give us much information concerning the 

 organs falling under this category ; he was further unfortunate 

 in his attempts to identify these badly preserved parts, and 

 consequently, beyond a slight knowledge of the gills, we were 

 quite in the dark as to the relations of the kidneys and the 

 genitalia, since the structures to which Dall, and after him 

 Fischer and Bouvier, applied these names, have quite different 

 significances. 



The Ctenidia. — The gills are very large and conspicuous, 

 and possess the form characteristic of the Scutibranchia 

 (figs. 5, 6, 7 and 14). The two gills, though symmetrically 

 placed, are not equally developed, that on the left side being 

 very much larger than that on the right (cf. figs. 5 and 7). 

 This is a very interesting feature, which is obviously con- 

 nected with the dextral coiling of the shell, and one which is 

 of great significance when studying the phylogeny of the 

 Azygobranchia. Each gill is characteristically bipectinate, 

 consisting of an axis which takes the form of a long and some- 

 what stout septum, containing the efferent and afferent bran- 

 chial vessels, and two sets of gill-filaments, which have the 



