PILSBEY : PHYLOGENY OF AEIONID^, 



97 



spines or other processes ; is less constricted mesially, and evidently 

 is somewhat more swollen distally, with a larger papilla. The 

 epiphallus is more kinked. The duct of the spermatheca is very 

 much shorter, the spermatheca itself longer. (2) In the muscles, the 

 pharyngeal reti'actor is not split to its base as Godwin- Austen's figure 

 shows; the retractor of the penis is not inserted to the right, but 

 to the left, of the pharyngeal retractor; and the ocular retractors 

 are more widely separated. 



These differences may be due to two causes : individual, or specific 

 variation, and inaccuracy of the published figures. The divergence 

 in proportions of the reproductive system I do not hesitate to attribute 

 to individual variation. The lack of calcareous spines in the basal 

 portion of the penis, as figured by Godwin-Austen, is probably due 

 to the state of the specimen ; mine being collected in October, when 

 the organs were probably not functionally active. Perhaps the 

 spines are broken off and lost during the period of reproduction, like 

 the darts of Helices ; although here the resemblance ceases, for I do 

 not see the slightest reason for considering these spines homologous 

 with true darts, as suggested by Godwin-Austen. 



Regarding the different arrangement of the muscles, and especially 

 the retractor of the penis, I can only suppose that Godwin- Austen 

 wrongly identified them. In no slug known to me is the retractor of 

 the penis inserted to the right of the pharyngeal retractor, as figured 

 by him ; and most assuredly this is not the case in the Anadenus 

 before me. 



With these matters explained, there is no reason against the 

 reference of this slug to A. altivagiis, Theob., as defined anatomically 

 by Godwin- Austen. So far as I can see, A. Sclilagintweiti^ Heyn., 

 has no differential characters, and is probably -identical. A. gig aniens 

 differs conspicuously in dentition, in the obsolescence of the ectocones, 

 and great length of the mesocones. A. Jerdoni, G.-A., A. Blanfordi, 

 G.-A., and A. modestus, Theob., are still unknown anatomically.' 



Judged by the arrangement of its retractor muscles, Anadenus 

 belongs to that division of Arionidse in which Arion, Geomalacus, 

 and Propkysaon are leading genera. It differs from all of these, 

 however, in possessing a normal penis. Arion and Geomalacus are 

 further removed from Anadenus and all other Arionidse by the more 

 posterior insertion of the pharyngeal retractor muscle, which has 

 moved backward from its normal position at the posterior edge of 

 the diaphragm, and by the arrangement of the intestinal tract, the 

 first posterior loop being decidedly the longest, while in Anadenus and 

 all other Arionidee it is the second posterior loop, that formed by G^ 

 and G\ which e.x.tends backward notably beyond the other. 



Anadenus, then, is a much more primitive genus than any of the 

 European Arionidpe. It resembles the American Prophysaon in its 

 muscles and has the same type of intestine, though somewhat longer 



' See Godwin- Austen's useful monograph, t.c, pp. 46-55, pis. vi, vii; and 

 Cockerell, Ann. and Mag. N. H., ser. vi, vol. vi, p. 277. 



