354 LITHOTRYA DORSALIS. 



The basal calcareous cup (fig. 1 d and 1 c) is well de- 

 veloped, and is sometimes even half an inch in diameter. 

 Before the cup is formed, there is a row of small, flat 

 discs (fig. 1, and like those in fig. 2 a) attached to the 

 sides of the burrow ■ but a full account of these parts of 

 the peduncle, and of the burrowing habits of this species, 

 has been given under the generic description. 



Size and Colour. — Full average-sized specimens have a 

 capitulum half an inch in width and height ; the entire 

 length, with the contracted peduncle, being about an 

 inch and a half. Valves coloured dirty white, with the 

 enveloping membrane, when preserved, yellow. The 

 outer maxillae, palpi, pedicels of the cirri, anterior faces 

 of the segments, dorsal tufts, caudal appendages, and 

 penis, dark purple. Thoracic segments brown. There 

 is a purple spot between the bases of the first pair of 

 cirri. 



Mouth. — Labrum considerably bullate, equalling about 

 half the longitudinal diameter of the mouth ; inferior part 

 produced so as to separate the mouth some way from the 

 adductor muscle ; crest with a row of blunt teeth and 

 hairs ; central part depressed and flattened. 



Palpi, rather large, separated from each other by only 

 half their own length; bluntly pointed, thickly clothed 

 with spines. 



Mandibles (PI. X, fig. 2), with twice as many pectina- 

 tions, namely 15, between the first and second main teeth, 

 as between the second and third teeth, namely about 7 ; 

 inferior angle strongly and coarsely pectinated ; distance 

 between the tips of the first and second main teeth, con- 

 siderably less than between the tips of the second tooth 

 and of the inferior angle ; sides hirsute. 



Maxilla (fig. 1 0), with the edge not quite straight, with 

 the whole inferior part slightly projecting; spines very 

 numerous, thirty or forty pairs ; those close beneath the 

 two upper great unequal spines, form a tuft and are rather 

 thinner than the others, as are also those near the inferior 

 angle; sides hirsute. 



