PILSBRT : PHXLOGEJSrr op AKIONID^, 95 



retractor {jjJi.r.), ocular and tentacular retractors (e.r.), retractor 

 of the penis {p.r.), retensor (ret.). The pharyngeal, pedal and 

 tentacular retractors are inserted proximally upon the columella in 

 snails, at or behind the posterior edge of the diaphragm upon the body- 

 Trail in slugs. Sometimes pharyngeal and ocular retractors tinite 

 posteriorly into one trunk (LimacidsB), sometimes remain separate 

 throughout (Arionidas, Philomycidte). From loss of function the 

 pedal retractor has degenerated in slugs, but the problematic muscle, 

 called by Simroth the retensor, is supposed by Mr. Vanatta and myself 

 to be perhaps the pedal muscle changed in position and function. 



In the more primitive genera of Arionidse, the pharyngeal and 

 ocular retractors converge posteriorly and are inserted in a compact 

 group (PI. YII, Fig. 4, Ariolimax) ; in the more modified genera 

 they are subparallel, with widely separated insertions (PI. YII, 

 Fig. 1, Anaclenus). Other details "will be found below.'- 



Before proceeding to discuss the classification of Arionidse, the 

 presentation of some notes on little-known genera may be permitted, 

 chiefly on account of the anatomy of A^iadenus. This interesting 

 Himalayan slug, rivalling the Ariolimaces in size, has been dissected 

 by Lieutenant-Colonel Godwin-Austen ; but since I am able to supple- 

 ment his account by descriptions and figures of the digestive system 

 and musculature, and since my observations upon some other points 

 do not wholly correspond with his results, it has seemed worth while 

 to give the anatomy as completely as I could work it out from the 

 single specimen at my disposal. 



Genus ANADENUS. 



The specimen examined was collected by M. M. Carlton on " Beas 

 River, thirty-five miles from the entrance of river into the plains, 

 within the lower mountains, October 4, 1870." ^ It measures 80 mm. 

 in length, the greatest breadth of its sole being 25 mm. 



Twenty-eight years in alcohol have not left much colour, but 

 what there is resembles Godwin-Austen's figure.^ The integument 

 of this specimen is remarkably loose and sack-like, so relaxed that 

 surface-markings are almost effaced. The foot-margin is narrower 

 than in any other slug of the family ; and no trace of longitudinal 

 division can be seen on the sole. The stout calcareous shell is broken, 

 but evidently was somewhat longer than the kidney. Semper's organ 



1 See also Pilsbry & Vanatta, Revision of American Slugs, II. The greater part 

 of our knowledge of slug musculature has hitherto been clue to Dr. H. Simroth, who 

 in several papers has described and figured the muscles of various genera ; and 

 though he has not incorporated myologic characters in his generic diagnoses, still 

 he treats them as of generic constancy. This estimate is fully supportedby our 

 own observations. The musculature shows but little variation within the limits of 

 a genus, and even affords family characters of high value. 



^ This is not far from Simla, toward the north. I owe to Professor A. Agassiz, 

 of the Museum of Comparative Zoology, the opportunity of dissecting this slug. 

 The preparations are now in that museum. 



2 Land and Fresh-Avater Mollusca of India, vol. i, pi. vi, fig. 1. 



VOL. III.— JULY, 1898. 7 



