Type-specimens of Poecilasma cariiiatum. 407 



than one-twelfth of the length of the peduncle of the sixth 

 cirri. 



The mandible has three teeth and a forked inner angle ; 

 the first cirri have eight segments in each ramus ; the poste- 

 rior cirri have four or five pairs of spines on the middle 

 segments, the proximal pair very small. 



This specimen doubtless represents a species distinct from 

 .1/. carinatum, but it is not so easy to be sure that it is 

 distinct from some of the other species of the subgenus, in 

 which the appendages have not been described. Since it is 

 solitary and probably immature, it seems inadvisable to 

 distinguish it by a new specific name. 



General Remarks. 



In establishing the genus Poecilasma, Darwin stated the 

 filamentary appendages were absent (Lepadidse, p. 100), and 

 the statement is repeated by Gravel and by Annandale. 

 Hoek does not mention these structures, and Pilsbry (15:111. 

 U.S. Nat. Mus. lx. 1907, p. 82) merely says of Poecilasma 

 " No lateral filaments at bases of the cirri," and does not 

 mention the character under Megalasma. There is evidently 

 considerable diversity as regards these appendages in the 

 species referred to Glyptelasma, and in some species they are 

 absent altogether, as they are in Poecilasma, s. str. They 

 may furnish characters valuable for the discrimination of 

 species in this group, subject to the caution suggested by 

 their known variability in size and number in the species of 

 Lepas (Darwin, Lepadidse, pp. 70—71). 



Aniiandale's transference of the subgenus Glyptelasma 

 from Megalasma to Poecilasma is not supported by the facts 

 here recorded. Apart from the carina, Megalasma is distin- 

 guished from Poecilasma by the form of the scuta, in which, 

 as Pilsbry expresses it, "there has been a rotation of the 

 basal margin of the scutum through 90°, bringing it in line 

 with the occludent margin/' The specimens discussed above 

 show intermediate stages between those in which the basal 

 margin is at right angles to the chord of the occludent 

 margin and those like the holotype of M. carinatum, in 

 which the two margins form a continuous curve. From 

 these to the typical forms of Megalasma the change is very 

 slight, and I therefore follow Pilsbry in including the species 

 of Glyptelasma in that genus. 



M. subcarinatum, Pilsbry, the. type of the subgenus, does 

 not differ greatly from Si. carinatum in the proportional 



