II— DESCRIPTION OF GENERA AND SPECIES. 



Lepas, Linn. (17G7). 



Darwin enumerates six species belonging to this genus, all of which, as a rule, are 

 found attached to floating objects, dead or alive. No new species of this genus has been 

 proposed since the publication of Darwin's Monograph, nor has our knowledge as to their 

 range been considerably augmented or altered. Five of the known species are found 

 nearly all over the world, the sixth, Lepas australis, Darw., inhabiting the whole circum- 

 ference of the Southern Ocean. 



No fossil remains of a species of this genus have hitherto been found; it seems to be 

 absent even from the newer Tertiary and Quaternary deposits. Perhaps this is because 

 the genus has originated since that time. However, it is also possible that the genus 

 existed in previous epochs, but that its attachment to floating objects was not favourable 

 to its being preserved in fossil deposits. The genera of Cirripedia, fossil remains of 

 which have been found as yet, are attached to fixed objects, and often are inhabitants of 

 deep water. 



It is by no means always easy to distinguish the species of this genus. From a 

 careful examination, however, I am convinced that the diagnoses as given by Darwin 

 are always sufficient. From these diagnoses I have composed the following table, which, 

 of course, does not include all the variations often very considerably changing the exterior 

 of some of the species. 



Lepas. 



1. Carina terminating in a flat oblong disc, . . . Lepas fascicularis, Ellis and Solander. 



2. Carina terminating in a fork. 



i. Valves furrowed. 



(a) Occlndent margin of the scutum arched, pro- 



tuberant, ..... Lepas anserifera, Linn. 



(b) Occludent margin close to the ridge from the 



umbo to the apex, . . . Lepas pectinata, Spengler. 



ii. Valves not furrowed. 



(a) Valves smooth or delicately striated ; internal 



umbonal tooth on the right hand scutum, Lepas anati/era, Linn. 



(b) Valves smooth; no internal umbonal teeth on 



the scuta, ..... Lepas hillii, Leach, sp. 

 Ic) Valves smooth, thin, brittle; internal umbonal 



teeth on both scuta, . . . Lepas australis, Darwin. 



