338 GENUS LITHOTRYA. 



of exuviation ; so also do the teeth or serrated margins 

 on the valves of the capitulum. Each scale has a fine 

 tubulus passing from the corium through the membrane 

 of the peduncle to its bluntly-pointed imbedded fang or 

 base. The membrane is transparent, thin, and tender, 

 to a degree I have not seen equalled in the other Lepa- 

 didae, except, perhaps, in Ibla. It is much wrinkled 

 transversely. 



Muscles of the Peduncle. — These consist of the usual 

 interior and longitudinal, — exterior and transverse — 

 and oblique fasciae ; the former are unusually strong ; 

 downwards they are attached to the basal calcareous cup 

 or disc, and upwards they extend all round to the lower 

 curved margins of the valves. They are, as usual, without 

 transverse striae. Besides these, there are, (at least in 

 L. dorsalis and L. Nicobarica,) two little fans of striae-less 

 muscles, which occur in no other pedunculated cirripede ; 

 they are attached on each side of the central line of the 

 carina, near its base; they extend transversely and a 

 little upwards, and each fan converges to a point where 

 the lower margins of the carina and terga touch ; of these 

 muscles, the upper fasciae are the longest. Their action, 

 I conceive, must be either to draw slightly together the 

 basal points of the terga, and so serve to open their 

 occluclent margins, or to draw inwards the base of the 

 carina : these muscles apparently first shadow forth the 

 posterior or carinal, transversely-striated, opercular muscles 

 of sessile cirripecles. 



Basal Calcareous dip or Discs. — I have seen this part 

 in all the species, except L. Valentiana, and in this it 

 probably occurs, considering its very close alliance with 

 L. truncata. The size, form, and conditions of the cup 

 or disc varies infinitely according to the age, size, and 

 position of the individual specimen. We will commence 

 with a full- sized animal, which has ceased to burrow 

 downwards into the rock, in which case the discs usually 

 grow into a cup, and become largely developed. In 

 L. dorsalis alone, I have seen many specimens, so that 



