28 PROCEEDINGS OF THE MALACOLOGICAL SOCIETY. 



Free muscles. — The retractor of the penis is long and inserted in the 

 floor of the pulmonary cavity. The two tentacular retractors seem 

 to be inserted independently on the columella, as in Epiphragmophora. 

 Both divide about midway into ocular and tentacular branches. 

 Strebel found no buccal retractor, but a very slender one, joining the 

 left retractor band, seemed to be present in the specimen I examined, 

 though it was broken, and I am not positive that I correctly joined 

 the loose ends (PL III, Fig. 15). 



The lung (Fig. 13) is short, with spongy reticulation, chiefly near 

 the breathing pore, adjacent to the commencement of the pulmonary 

 vein. Heart on the left side of the kidney, which is excavated to 

 accommodate it. Kidney large and squarish. I did not find the 

 ureter. 



Of former accounts of the anatomy of Xanthonyx, it may be said 

 that Fischer's preparation of the genitalia was mutilated, and part of 

 the structures wrongly interpreted. The specimen was probably 

 preserved in alcohol after old-time methods. Strebel and Pfeffer 1 

 have given a very good account of the genus. They figure and 

 describe large shell-lobes to the mantle, but these are almost obsolete 

 in my specimen. The ducts of the mucous glands are longer in their 

 figure than in my preparation, and the dart-sac (which they do not 

 recognize as such) is smaller. The exterior is dark-coloured, while 

 my specimen is nearly white. These differences are probably specific, 

 Strebel and Pfeffer having dissected X. Cordovanus, while my specimen 

 seems referable to X. Salhanus. 



The relationship between Xanthonyx and Metostracon has already 

 been alluded to. One of the most striking features of Xanthonyx is 

 the removal of the ducts of the mucous glands from their typical 

 position upon the dart-sac to an intermediate station between the sac 

 and the vagina, the insertions being directly at the junction of these 

 organs. No similar case is known in the Asiatic Belogona Euadenia, 

 but in America we find the same arrangement in Micrarionta, and in 

 Lysinoe the tendency has gone further, and the mucous glands are 

 wholly removed from the dart-sac and inserted upon the vagina. 

 This is a process quite parallel to what has taken place in the 

 Belogona Siphonadenia of Europe. 



Whether Xanthonyx will prove to have a relative in Cryptostracon 

 remains doubtful ; but the latter genus may well be a more advanced 

 member of the same phylum. It may therefore be well to recall our 

 scant knowledge of the group. 



CEYPTosTKACoisr, "W. G. Binney. 



Annals of the New York Academy of Sciences, i, p. 258. 

 This genus is completely slug-like, with rather small mantle and, 

 according to Binney, completely enclosed shell. The breathing orifice 

 is slightly in advance of the middle of the right margin of the mantle ; 



1 " Beitrag zur Kenutniss Mexikanischer Laud- unci Siisswasser- Couch vlieu," 

 licit i'v, p. 26, pi. x, f. 7. 



