328 BULLA. 



Gizzard containing three subequal nearly similar horny or ehiti- 

 noid plates which are dumb-bell shaped on the outer surfaces (pi. 

 48, fig. 15) the inner or grinding surfaces being somewhat truncated 

 wedge-shaped with flat tops (fig. 17). The side view (fig. 16) 

 shows a ledge (where the muscles of the stomach-wall are attached) 

 separating the outer face from the grinding face. The figures repre- 

 sent the plates of B. nebulosa Gld. Those of B. ampulla are shorter, 

 with the external processes nearer together. 



Radula (pi. 48, fig. 4, B. ampulla) large, with dark chitinous 

 teeth according to the formula 1"2'1'2"1. Laterals not diflferentiated 

 from uncini. Rhachidian teeth like a transverse bar, its reflexion 

 bearing numerous denticles of which the median one is smaller. 

 Laterals claw-shaped, with about 6 long denticles. Outside of the 

 second lateral lies. a small, thin basal-plate without cusp, the rem- 

 nant of a third lateral tooth. In B. nebulosa Gld. this plate is larger 

 and thicker, but still lacks the cusp. B. striata presents a radula 

 and gizzard-plates of the same type. 



The Linna3an genus Bulla consisted of species of the genera Ovula, 

 Physa, Auricula, Melampus, etc., besides the tectibranchiates then 

 known. Bruguiere in the Encyclopedic Methodique eliminated all 

 but the last, which form a perfectly natural group. Finally Lam- 

 arck, in the Systeme des Animaux sans Vertebres, 1801, cites only 

 B. ampulla L. as an example of the genus, thus fixing that species 

 as the type. The attempts of Menke, Morch and others to substitute 

 other names for the typical group of species, are therefore without 

 basis. 



"The species of this geuus inhabit sandy mudflats, the slimy 

 banks of river-mouths, and brackish places near the sea ; at low- 

 water some of them conceal themselves in the mud and under sea- 

 weed, exuding large quantities of mucus to maintain the moisture 

 of their skin. The shells of Bidla, as restricted, are rather solid, 

 smooth, and marbled and mottled like birds eggs." (JFf. & A. Ad.) 



The gizzard of a specimen of B. nebulosa Gld. examined by my- 

 self contained a mass of vegetable fibers, probably algpe, but no 

 animal remains. 



Species of the Mediterranean, Atlantic and 



Gulf of Mexico. ^ 



The littoral Bullas of this area form a very difficult assemblage, 

 requiring a great mass of material for its elucidation. The creatures 



