540 
Proceedings of Royal Society of Edinburgh. [sess. 
ings towards the centre 3, increasing outwards to 2, at the border 
8 in *01 mm., forming 3 concentric zones. 
Habitat. — Mors deposit (Grunow). 
Var. gelida. Grun., ibid., 1884, p. 74, pi. iii. (C), fig. 6. — Diam. 
•114 mm. Markings increasing, hut little from the centre outwards ;• 
towards the centre 3, towards the border 2f, at the border 7, in 
*01 mm. 
Distinguished from var. morsiana by the markings towards the 
border, and from C. apiculatus, var. Woodwardii, by the increase of 
the markings outwards. 
Habitat. — Franz Josefs Land (Grunow). 
Var. algida. Grun., ibid., 1884, p. 74, pi. iii. (C), fig. 5. — Diam. 
*094 mm. Central smooth area small. Markings subequal, 2 to 
2i in -01 mm., at the border 3 \ in ’01 mm. 
This var. approaches C. marginatus in the character of the 
markings. 
Habitat. — Franz Josefs Land (Grunow). 
C. heteroporus. Ehrb., Mon. Ber. Ah., 1844, p. 265. — Diam. 
•072 to T125 mm. Central space small, or replaced by a small 
rosette. Markings at the centre 3^ to 4, increasing outwards to an 
annular, somewhat elevated area about the semiradius to 2 or 21, 
again decreasing to the border to 6 or 7 in ’01 mm.; rows sometimes 
indistinctly radial ; secondary oblique rows irregular, obscure. 
Border striae evident, 6 in -01 mm. — Balfs in Pritch. Inf., p. 831; 
Grun., Denk. Wien. Ah., 1884, p. 74. C. heteroporus, var. Grun., 
in Sch., Atl., pi. lxi. fig. 4. 
Recent Manilla valves show a transition to C. apiculatus, var. 
Woodwardii. It differs from C. crassus in the less robust appearance 
of the markings and the distinctly striated border. 
Habitat. — Nottingham and Monterey deposits (Grunow); Elephant 
Point, Bengal (Grunow); Piscataway deposit (Griffin!); Santa 
Monica deposit (Rae !) ; Delaware, Maryland (O’Meara!); Manilla 
(Grove !) ; Labuan (Cleve !) ; Maryland (Cleve). 
Var. moronensis. Grun., Denk. Wien. Ah., 1884, p. 75. — Diam. 
T mm. Central rosette distinct. Markings on the elevated ring 
