542 THE MICROSCOPE. 



like membrane, which lies folded up in the abdominal 

 cavity, is furnished with numerous rows of strong, nearly 

 opaque, dark brown tricuspid teeth. The teeth of Acmcea 

 (No. 117) are differently arranged ; their formula is 3 1 3. 

 Chitonidce are said to be near relatives of the Patellidce ; the 

 mouths of all are furnished with mandibles. 



Testacella maugei, belonging to the Pulmonifera, is slug- 

 like in its appearance, and, curiously enough, is subter- 

 ranean in its habits, chiefly feeding on earth-worms. During 

 winter and in dry weather it forms a kind of cocoon, 

 and thus completely encloses itself in an opaque white 

 mantle, which effectually protects it from atmospheric 

 influences. Its lingual membrane is large, and covered 

 with about fifty rows of divergent teeth, which gradually 

 diminish in size towards the median row ; each tooth is 

 barbed and pointed, broader towards the base, and fur- 

 nished with an articulating nipple set in the basement 

 membrane. A few rows are represented slightly mag- 

 nified, Plate V. No. 121. Their formula is 1 0. 



Gymba olla (the Boat-shell) belongs to the species 

 Velutinidse, formula, 1 * 0, or 1 1 1. The lingual band, 

 No. 118, is narrow and ribbon- like in its appearance, with 

 numerous trident-shaped teeth set on a strong muscular 

 membrane. The end of the strap and its connexion with 

 the muscles at the hinder extremity of the cartilaginous 

 cushion is shown in the drawing. The blueish appearance 

 seen in the Plate is due to a selenite film and polarised 

 light. Scapander ligniarius (the Boatman shell). The 

 band (Plate V. No. 119), is narrow, but the teeth are bold 

 and of extraordinary size ; their formula is 1 1. This 

 mollusc is said to be without eyes. Pleurobranchus plu- 

 mula belongs to the same family ; its teeth are simple, re- 

 curved, and convex, and arranged in numerous divergent 

 rows ; the medians of which are largest. The mandible 

 (Plate Y. No. 122), presents an exceedingly pretty tesse- 

 lated appearance, and the numerous divergent rows have 

 tricuspided denticulations. Velutina loevigata (the Velvety 

 shell), formula 3 1 3. The teeth (Plate V. No. 108) are 

 small and fine ; medians recurved, with a series of deli- 

 cate denticulations on either side of the central cusp, 

 which is much prolonged : 1st laterals, denticulate, with 



