72 GENUS — LEPAS. 



Distribution. The species abound over the arctic, 

 temperate and tropical parts of the Atlantic, Indian and 

 Pacific Oceans, and are always, or nearly always, attached 

 to floating objects, dead or alive. The same species have 

 enormous ranges ; in proof of which T may mention that 

 of the six known species, five are found nearly all over the 

 world, including the British coast ; and the one not found 

 on our shores, the L. australis, apparently inhabits the 

 whole circumference of the southern ocean. 



General Remarks and Affinities. — The first five species 

 form a most natural genus ; they are often sufficiently diffi- 

 cult to be distinguished, owing to their great variability. 

 The sixth species (Z. fascicularis) differs to a slight 

 extent in many respects from the other species, and 

 has considerable claims to be generically separated, as 

 has been proposed by Mr. Gray, under the name of 

 Dosima ; but as it is identical in structure in all the 

 more essential parts, I have not thought fit to separate it. 

 As far as external characters go, some of the species of 

 Paecilasma have not stronger claims, than has L. fascicu- 

 laris, to be generically separated ; and I at first retained 

 them altogether, but in drawing up this generic descrip- 

 tion, I found scarcely a single observation applicable to 

 both halves of the genus ; hence I was led to separate 

 Lepas and Paecilasma. If 1 had retained these two genera 

 together, I should have had, also, to include the species 

 of Dichelaspis and Oxynaspis ; and even Scalpellum 

 would have been separable only by the number of its 

 valves ; this would obviously have been highly inconve- 

 nient. Although some of the species of Peecilasma so 

 closely resemble externally the species of Lepas, yet if we 

 consider their entire structure, we shall find that they are 

 sufficiently distinct; as indirect evidence of this, I may 

 remark that Conchoderma (as defined in this volume), 

 includes two genera of most authors, and yet certainly 

 comes, if judged by its whole organisation, nearer to 

 Lepas than does Paecilasma. 



