Revision of the 6''e/iU5 Lomanotus. 215 



its description the original descriptions of the remaining 

 five, omitting most of the purely generic characters and 

 all specific characters derived from colour, the evidence will 

 present itself in its clearest form. None of the six species 

 is better suited for this purpose than L. genei, as none has 

 been more fully described from mature examples. Let this, 

 then, be taken as the standard, and the following table will 

 exhibit all the structural diflferences which can be adduced as 

 justifying the retention of the remaining five species. Yerany's 

 character of the genus, drawn from the ' Revue Zoologique ' 

 of 184-4 and the Acts of the Milan Congress of the same year, 

 published in 1845, is placed at the head of the table for 

 reference. 



Loi£A>-OTrs, Veranv (1844). 



Body oblong, wedge-shaped : head as wide as the body, furnished with 

 4 small tentac aliform prolongations ; dorsal tentacles 2, retractile, club- 

 shaped, laminate, each included in a calycif orm sheath ; branchife formed 

 of 2 irregidarlv fringed and festooned membranes, attached longitudinally 

 one to each side of the dorsal surface and to the tentacle-sheath ; anal and 

 genital orifices on the right side. 



L. genei, T(?rany. — Sheath-margins 4-lobed ; pleuropodium reaching 

 almost to the tail on either side. 



L. marmoratus (Alder k Hancock). — Sheath-margins entire ; pleuro- 

 podiimi not connected with the sheaths, but produced forwards in 

 front of them. • 



L. Jlavidus (Alder & Hancock). — Sheath-margins tubercled: pleuro- 

 podium indistinct, its place marked by a marginal series of 

 unequal-sized papillae. 



L. port land iois, W, Thompson. — Sheath-margins diyided into six finely 

 pointed filaments : pleuropodium " commencing in front of the base 

 of the sheaths and continuing behind the termination of the tail." 



L. hancocJii, Xorman. — Sheath-margins with 5 diyisions : rhinophores 

 little longer than the sheaths, not laminated. 



L. eisigii, Trinchese. — Pleuropodium continuous round the body from 

 sheath to sheath, its two lateral sections uniting at the apex of the 

 tail and forming there a fin-like swimming-organ. 



At a first glance it would seem as if specific value might 

 fairly be conceded to tiie structural distinctions shown in this 

 table. But when we come to examine into their claims more 

 narrowly in the light of the facts brought out by the chrono- 

 logical survey just given, it will be seen that many of these 

 characters lack the necessary certainty and permanence. In 

 studying a group of soft-bodied animals such as the Nudi- 

 branch Mollusca, endowed, and often to a high degree, with 



