120 Deniition of Pulmonate Mollusks. 
plate-like sections, of the character found in the jaws of Cylindrella, Macro- 
ceramus, and many species of Bulimulus. No appearance of triangular upper 
median plates, however, as in Cylindrella, though the two specimens ex- 
amined by me are not perfect at that part. Both margins serrated by the 
extremities of the ribs. The jaw is quite membranous. 
Lingual membrane (PI. XIII, fig. E). Centrals subquadrate with a very 
large, stout, short, pointed cusp, the side cusps obsolete. Laterals larger 
and more narrow than the centrals, bicuspid, the inner cusp greatly pro- 
duced, broad and quite squarely terminating. The base of attachment of 
the laterals is cut away on the inner side, leaving a large outer lateral ex- 
pansion, bringing to mind the much less developed one of Succinea, 
Marginal teeth quadrate, gradually becoming modified from the laterals, 
the cusps finally passing off into simple, obtuse papillee, the inner one the 
larger. 
Bulimulus. 
The species of this genus may be grouped by their lingual 
dentition, independently of the character of the shell, into 
(a) those having the type of teeth usual in the Helicidw, and 
(4) those haviug the peculiar type of dentition figured on PIL. 
XII, fig. G (see B. primularis), and (c) those having the denti- 
tion of B. Lobbi. (Pl. XIV, fig. H.) . The former two types are 
found in several of the subgenera noticed below. 
The jaw of Bulimulus is usually thin, with delicate, separated 
ribs as in Oylindrella, their ends serrating either margin; the 
ribs at the upper centre of the jaw often run obliquely and ter- 
minate before reaching the lower margin. 
Drymeus altoperuvianus, Rve. Between Balsas and Caja- 
marca, Peru. “Prof, Oton. 
Jaw with 31 ribs, delicate, separated, as in Cylindrelia. 
Lingual membrane (Pl. XIV, fig. F) very peculiar, resembling that of 
B. Lobbi, described below, excepting that the marginal teeth are of same 
type as the laterals, with still more produced cutting point; one in profile 
is Shown in the left-hand figure. 
Drymeus Vincentinus, Pfr., var.? ‘Tobago. 
Jaw as usual in Bulimulus, thin, transparent, with numerous delicate, 
separated, narrow ribs. 
Lingual membrane as in Bulimulus laticinctus. (See below.) 
Dryneus Knorri, Pfr. Porto Cabello, Venezuela. Mr. Robert 
Swift. 
