6 SYSTEMATIC ARRANGEMENT 



t. 36. f. 15, are represented as having a corrugated muzzle and lateral 

 tentacula, as if they had no trunk ; they differ in this respect from the 

 other figures of the same species at fig. 13, where the tentacles are 

 properly represented as close together at their base. 



1. Acus. 



Tentacles small. Suture of shell simple. Operculum ovate ; nu- 

 cleus apical. 



1 . A. maculatus, t. 85 a. f. 8, t. 99. f. 1 ; Adams, Gen.Moll. t. 24. f. 1 . 



2. A. subulatus, t. 99. f. 3 ; Adams, Gen. Moll. t. 24. f. 2. 



Tentacles of Acus maculatus very small, short, cylindrical, nearly 

 close, with verysmall eyes at the apex. Mantle simple. Siphon broad, 

 rather short. Foot folded down on each side in front when contracted. 

 Proboscis elongate, thick, entirely retractile. Lingual membrane and 



teeth 1 Operculum ovate, trigonal, nearly flat, with a subcen- 



tral longitudinal ridge, brown ; apex subacute ; nucleus apical. 



The mantle of Acus maculatus is enclosed. Siphons elongate, 

 conical, when contractile spirally curved. Tentacles very small, 

 nearly close together at their base, short, cylindrical, blunt, with the 

 eyes at their tips, without any veil. Proboscis very long, cylindrical, 

 with a large longitudinal mouth. Lingual membrane an d teeth 1 



2. Subtjla. 



Tentacles and eyes none. Suture of shell simple. Operculum 

 ovate. Nucleus apical. 



1. S. ? anatomy, t. 99. f. 2. 



2. S. dimidiata, t. 99. f. 4. 



3. S. strigilata, t. 85 a. f. 9. 



Foot of Subula dimidiata moderate ; folded across. Operculum 

 horny, lanceolate. Head indistinct ; only an aperture for the emission 

 of the proboscis. Tentacles none. Eyes none. Mantle enclosed. 

 Siphon elongate, spirally twisted when retracted into the shell. 



3. Leiodomus. 



Tentacles small. Operculum ovate. Suture of shell callous, like 

 Bullia, but foot small. 



1. L. ceeruleus. 



Foot of Leiodomus ccerulescens moderate, folded longitudinally in 

 front. Mantle enclosed. Siphon rather elongate, crenulated on the 

 lower edge. Tentacles very small, very short, subcylindrical, with 

 the eyes on their tips, placed on each side of the contracted cavity for 

 the emission of the proboscis, without any veil. Proboscis elongate. 



Lingual membrane ? Male organ elongate, subcylindrical, on 



hinder part of right side. Operculum ovate, much smaller than 

 aperture of shell, blunt at each end, annular, thick ; nucleus suban- 

 terior, on front of inner side. 



According to the observations of M. Morch, Leiodomus cinereus 



