18G7.] DR. J. E. GRAY ON CATILLUS. 995 



marginal process. The outer surface of the shelly part of the oper- 

 culum is generally radiately and concentrically striated, and furrowed 

 with two more or less distinct ribs radiating from the nucleus to the 

 outer edge ; the ribs across the middle of the plate generally end in 

 a rounded lobe ; that on the right margin of the plate is much more 

 distinct, narrow, linear, and ends in a projecting spine. The inner 

 surface of the plate is smooth, or with a few concentric marks show- 

 ing how the shelly matter was deposited as the plate increased in 

 size and thickness. The shelly plate of the operculum in the larger 

 number of species is more or less quadrangular, with the horny 

 operculum oblong, occupying the broadest part of the base and 

 forming a fringe to that edge. In others the shelly plate is oblong 

 elongate, with the horny operculum triangular, and occupying one 

 of the halves of the lower half of the entire operculum. 



Tribe I. Catillina. Operculum subquadrangular ; the horny 

 (true) operculum oblong, transverse, occupying the broader 

 end ; the other more or less dilated, two-lobed, the marginal 

 lobe acute, linear. Shell elliptical, mouth wide. 



1. Catillus. 



Shell elliptical, mouth wide ; inner lip flat, shelving, transverse, 

 or slightly regularly arched ; operculum shelly plate subquadran- 

 gular. 



A. The operculum as broad as long ; the right rib well marked, se- 

 parated from the margin by a granular space, which is broader 

 near the nucleus ; the right edge near the base denticulated ; 

 the nucleus rugose, granular ; the terminal lobes unequal — 

 one broad, the other linear, spine-like. (Figs. \a, \b.) 



Fig. 1 a. Fiff. 1 b. 



Fig. Ir^ Outer surface. Fig. 16. Inner surface. 



* Operculum large, thick, dark coloured, 



1. Catillus janelli. Reeve, Icon. f. I. (Operculum, Fig. l.) 

 Hab. Philippines. 



** Operculum moderate, thin. Eiana. 



2. Catillus clvpeolum. Reeve, Icon. f. 24. 



Catillus affinis, Reeve, Icon. f. 1.5. 

 Hab. Philippines. 



