140 GENUS CONCHODERMA. 



only fill the peduncle, but extend in a thin sheet between 

 the two folds of coriuni all round the sack, close up to 

 the terga. The two ovigerous fraena are present in the 

 usual position ; the ovigerous lamellae either form several 

 layers, in pairs, one under the other, or are united in a 

 single large cup-formed sheet enclosing the whole animal. 



Colours. — The prevailing tint is a dark purplish- 

 brown, which forms, or tends to form, broad longitudinal 

 bands on the peduncle and capitulum. 



General Remarks. — This genus is intimately related, 

 as has been remarked by Professor Macgillivray,* to 

 Lepas : if we look to the body of the animal, which from 

 being less exposed to external influences must, in the 

 Cirripedia, offer the most trustworthy characters, we find 

 that in Conchoderma there are additional filamentary ap- 

 pendages attached to the cirri, that there are no caudal 

 appendages, that the teeth of the mandibles are finely 

 pectinated, and that the ovarian tubes run higher up round 

 the sack ; in every other respect, there is the closest simi- 

 larity, even to the arrangement of the bristles on the 

 cirri. In the capitulum, the difference consists chiefly, 

 though not exclusively, in the less development of the 

 valves, and their consequent wide separation : the scuta, 

 however, in Conchoderma, are added to beneath their 

 u unbones, or original centres of growth, which is never the 

 case, or only to a very slight degree, in Lepas. Concho- 

 derma has no very close affinity to any other genus. As the 

 majority of authors have ranked the two common species 

 under two distinct genera (Otion and Cineras), I may 

 observe, that there is no good ground for this separation ; 

 in the above few specified points in which Conchoderma 

 differs from the genus most closely allied to it, the two 

 species essentially agree together. If we take the nearest 

 varieties of C. virgata and C. aurita, there is but a very 

 slight difference even in the form of their valves, and 

 these hold the same relative positions to each other ; the 



* Remarks on the Cirripedia, &c.; ' Edin. New Phil. Journal/ vol. xxxix, 

 p. 171. 



