AVOODWARD : ANATOMY OF ABEOEBIS. 141 



animal shows great activity, creeping about rapidly, and moving 

 its snout from side to side in its search for food. Duprey [1] speaks 

 of it swimming at the surface of the water, by which I presume 

 he means creeping, as a pond snail does by breaking through the 

 surface film, but this habit I never observed in Adeorhis. 



The animal is represented in the extended condition in Fig. 1 

 (PI, VIII), which drawing is constructed from my studies of the 

 live animal. 



Living specimens of AdeorMs were examined by Deshayes [2], 

 who, however, gives no description of it. A live specimen was also 

 studied by Marshall [3], who, according to Jeffreys, described it as 

 " so red that it seemed to stain his fingers." None of my specimens, 

 however, exuded any such colouring matter. 



The two best accounts of the external form of Adeorhis are those 

 of Duprey [1] in 1876 and Fischer [4] in 1885, and of these the 

 former is by far the most complete. Since, however, my observations 

 differ somewhat from those of both these investigators, I have thought 

 it advisable to give a short description of the external characters as 

 noted in my three living and active specimens, 



External Characters of the Living Animal. — The foot, which is of 

 a pale transparent flesh colour, is expanded and slightly notched in 

 front, each of the antero -lateral angles being produced out into a lobe, 

 recalling the condition seen in Valvata (Bernard [6] ). These lobes, 

 however, disappear when the foot is fully expanded, in which condition 

 it is of oblong fonn, slightly narrowing posteriorly and ending in 

 a bluntly rounded extremity ; in front it exhibits that curious double 

 margin (possibly the last trace of the propodium) so common among 

 the Prosobranchiata. A pedal gland opens ventrally near the front of 

 the foot. The operculum (PI. YIII, Fig. 2) is thin, transparent, 

 paucispiral, and littorinoid (see Jeffreys [6] ), and borne on the 

 posterior part of the foot (which does not exhibit an opercular lobe 

 or tentacle such as seen in Eissoia), behind which it projects on the 

 right side in Fig. 1 , though when the animal is fully expanded the foot 

 extends some distance behind the operculum. 



The snout or proboscis is fairly long, club-shaped, and non- 

 introvertible. Through its transparent walls the brick-red, muscular 

 buccal mass can be seen. It is flexed downwards somewhat, much 

 as in Vivipara, and the slit-like terminal mouth is consequently 

 ventral in position. On either side of the snout is situated a very 

 long, thin, and slightly club-shaped tentacle ; these are attached to 

 the head above the snout. Mr. Sykes, in a drawing which he made 

 from the living animal, has indicated a series of hair-like processes 

 covering the swollen end of the tentacle; these I was unable to 

 observe in any of my specimens, but their occurrence even in a single 

 specimen is of interest, because in Rissoia parva the tentacles are 

 conspicuously clothed with such processes. The eyes, according to 

 Fischer and Duprey, are very small, and situated at the outer base 

 and somewhat behind the tentacles. Examination of the living animal 

 led me to the belief that the eyes were wanting, but subsequently, 

 on teasing out a specimen in glycerine and examining it under 



