2IO Quarterly Journal of Conchology. 



By comparing the opercula of various Viviparidce in my collec- 

 tion, I find that of Tulotoma to be most nearly allied to that of 

 Lioplax, both in form and manner of growth. The reflected edge, 

 however, is distinctive, as is the fact that the opercula are always 

 bent, laterally, so that the extremities curve upward Avhen the 

 operculum rests upon the outer surface. This prominence has 

 been given to the description of the operculum, because of its high 

 office as a protective organ, and the fact that it is almost identical 

 in the three species of Tulotoma. 



It will be remembered that Prof Haldeman's description of the 

 genus begins with the words, "Soft parts of the animal and lingual 

 dentition unknown." These were described by Mr. W. G. Binney 

 in Annals of the Lyceum of Natural History, Vol. ix., February 

 1S70, as follows. "Foot moderate; not produced beyond the 

 snout. Color dark blue. Head and snout small. Right tentacle 

 broad. Left cervical lappet small; right larger, trough-shaped. 

 Branchial lamince numerous, long, narrow, crowded in a double 

 rOW. Lingual membrane long, with the arrangement of teeth usual 

 to the family. Teeth 3.1.3. The centrals are subcircular, ^^ith 

 a truncated, irregularly horizontal base; the apex recurved, chan- 

 neled and obtusely knobbed or denticulated. ' The first lateral is 

 about as wide as the central, oblong, bulging at the sides, truncated 

 and horizontal at tlie base, its apex deeply digitated or fringed, 

 some of the dc;nticles being recurved at their apices. The second 

 lateral is laminar, narrowing slightly towards the truncated base, 

 curving outward from the central tooth, its apex with long fringe- 

 like denticles, some of which are recurved, ethers obtusely knobby. 

 Th^ third lateral resembles in shape and size the second, but is 

 somewhat less curved, and has shorter, less delicate denticles. 

 There is considerable variation in the number, length, delicacy and 

 arrangement of the denticles on the different teeth. In some cases 

 they are very broad, with simple, recurved edges. In others they 

 are long, narrow and bifurcate. Again on many teeth the denticles 



