227 



domei form. It is not explained by senility, for in young 

 individuals an equal disparity is seen. 



It may attain a height of 50 mm., a length of 51 mm., 

 and a section of 35 mm. 



The ribs differ. Generally they are broad and rounded, 

 wider than the interspaces, which are deep and flat, with 

 vertical sides. But sometimes the ribs are low and wide, and 

 touch one another, so as to have no intervening squarely- 

 ploughed furrow. The concentric sculpture usually consists 

 of flattened contiguous plates on the ribs, while in the inter- 

 costal spaces there are low, vertical, thin lamellae. But it 

 may be no more than crowded concentric lirae, both on the 

 eostae and between them. 



The "lunular area" referred to by Angas is on the pos- 

 terior side of the shell, and therefore does not correspond 

 with the lunule of such shells as Chione. It may be very 

 defined, or only slightly marked or absent. 



Not a few individuals, after reaching a diameter of 25 

 mm., cease to grow in superficial area, but increase in sec- 

 tional diameter, while they actually decrease in their umbo- 

 ventral : so that their margin becomes curiously incurved and 

 their walls very thick, as figured in pi. xxviii., fig. 4. 



As to ornament, some shells in life are nearly white 

 without and quite white within ; others are of an almost uni- 

 form cinnamon-brown. The usual colour is a dirty-greyish or 

 very faint rusty tint, with rather reddish-rusty indistinct 

 blotches, disposed in irregular and broken cencentric lines ; 

 but they may have a pure white-gi'ound colour, marked with 

 long radial, dark purple-brown spots, variously disposed in 

 patterns, or scattered, or coalescing into a large area over 

 the ventral part of the posterior half of the shell. 



So within, some are quite white ; others have a dark- 

 brown line along the pallial margin, and edging each adduc- 

 tor scar ; others have the muscle-scars and the greater part 

 of the interior of a dark purple-brown. 



The extent to which the muscle-scars, anterior or pos- 

 terior, are supported by a callosity also differs greatly. 



There is every combination of the above-named differ- 

 ences, so that no true varieties can be established : only in- 

 dividual variations are recognized. 



Qlycimeris sordidus, Tate. 

 Pecfunculus sordidus, Tate, Trans. Roy. See. S. Anstr.. 1891, 

 vol. xiv., p. 264, pi. xi., f. 8. Type locality, St. Vincent Gulf, 9 

 to 11 fathoms, alive (Verco). I have taken it since in numbers in 

 Hardwicke Bay, in Backstairs Passage, and in Investigator 

 Strait, at all depohs from 13 to 22 fathoms. 



Professor Tate had only an immature individual from 

 h2 



