216 Mr. N. Colgan — Contributions towards a 



the power of expanding and contracting their tissues and of 

 renewing lost or injured processes, it is only too easy to fall 

 into errors of observation even when dealing with mature and 

 perfect examples; it is extremely difficult to avoid such errors 

 when the material is immature and defective. I shall not be 

 wanting, then, in respect for the authors of the splendid 

 ' Monograph of the British Nudibianchiate Mollusca ' if I 

 express the conviction that the peculiar structure of the 

 pleuropodium shown in their plate of L. marmoratus is due 

 to an error of observation. Verany, so early as 1845 (* Atti 

 della Sesta Riunione degli Scienziati Italiani'), mentions the 

 attachment of the pleuropodium to the rhinophore-sheath as 

 one of the characters of his genus Lomanotus, and subsequent 

 research has shown that this attachment is properly generic. 



As for the form of the sheath-margins, this is too variable 

 to afford a satisfactory specific character. In the Bullock 

 specimen described at the opening of this paper, for instance, 

 the irregularity of one of the sheath-margins was such as to 

 make it a matter of uncertainty whether its lobes or tuber- 

 culated divisions should be taken as four or five in number 

 (the almost simple margin of the other sheath was probably 

 due to accidental loss of the appendages). Again, some of 

 Mr. Garstang's specimens captured at Plymouth in 1890 had 

 the sheath-margins produced into four, five, or six irregular 

 processes, while of the larger specimen taken in the preceding 

 year he says that the sheath-margin had five or six blunt 

 prominences or tubercles, the precise number of the marginal 

 lobes being in this case apparently as hard to make out as in 

 the Bullock specimen. Not only does the number of divisions 

 in the sheath-margins vary, but, as Mr. Gamble has pointed 

 out, their form in the same individual is variable, since the 

 tubercular lobes are capable of contraction and dilation. It 

 seems clear, then, that L. marmoratus, described from a single 

 injured and apparently immature specimen, cannot be separated 

 as a species from Verany's L. genei by any certain structural 

 character. 



The claims of L.flavidus to specific rank may be more 

 summarily dealt with. It is obviously an immature form of 

 Lomanotus in one of the early stages of growth described by 

 Trinchese in his paper on L. eisigii, the stage when the 

 rhinophore-sheath has just been formed, while the pleuro- 

 podium remains as yet undeveloped. It would be idle to 

 speculate as to what final form might have been assumed by 

 this immature specimen of Alder and Hancock. It might 

 have grown into the likeness of Thompson's L. portlandicus ; 



