OCR Text |
Show 1867.] DR. j. E. G R A Y O N CATILLUS. 995 marginal process. The outer surface of the shelly part of the operculum 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 showing 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 subquadranyular; 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, separated 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, la, lb.) Fig. la. Outer surface. Fig. 16. Inner surface. * Operculum large, thick, dark coloured. I. CATILLUS JANELLI, Reeve, Icon, f, 1. (Operculum, Fig. 1.) Hab. Philippines. ** Operculum moderate, thin. Eiana. 2. CATILLUS CLYPEOLUM, Reeve, Icon. f. 24. Catillus affinis, Reeve, Icon. f. 15. Hab. Philippines. |