ON CRUSTACEA BROUGHT BY DR WILLEY FROM THE SOUTH SEAS. 673 



present specimen the flattened back of the segment in question has twenty-three pairs 

 of indents, not quite evenly or symmetrically spaced, but covering the whole length. 



The specimen is 135 mm. in length, the genital segment being about thrice as 

 long as the anterior part, and about twice as long as the terminal appendages. The 

 segment preceding the genital overlaps it with its lateral lobes and is dorsally coalesced 

 with it, so that it is difficult to give exact proportionate measurements. The egg-sacs 

 reach a length of 2.5 mm. or more. 



Heller's specimens, 12 mm. long, were from the gills of an Atlantic Coryphaena; 

 Bassett-Smith's, 10 mm. long, were found attached to the gills of Thynnus macropterus 

 at Aden ; the labels with the present specimen explained it to be a Lernaeid from 

 the gills of Bonito, Uvea, Loyalty Islands. 



THYPtOSTRACA. 



(CiRRIPEDIA.) 



Fam. Lepadidae. 

 Gen. Poecilasma, Darwin. 



1851. Paecilasma, Darwin, Lepadidae, Ray Soc, p. 99. 



188.S. Poecilasma, Hoek, Challenger Reports, vol. 8, Cirripedia, p. 44. 



1893. Poecilasma, Aurivillius, K. Svenska Vet.-Akad. Handl, vol. 26, No. 7, p. 9. 



Darwin, who rejected Trilasmis, Hinds, 1844, as an impossible name for a genus 

 in which the valves might be five or seven as well as only three, spells the new 

 name Paecilasma, but, as he derives it from 'jroiKi.Xo'i (printed Tro/ctXo?), the change 

 of diphthong subsequently adopted is obviously proper. 



Poecilasma vagans, Aurivillius. 



1892. Poecilasma vagans, Ofversigt af K. Svenska Vet.-Akad. Fiirh., No. 3, p. 123. 



1893. Poecilasma vagans, Aurivillius, K. Svenska Vet.-Akad. Handl, vol. 26, No. 7, 

 p. 9, pi. 1, figs. 9—12; pi. 8, figs. 10, 16, 22. 



Of Darwin's species only one, Poecilasma fissum, has seven valves. All the four 

 added to the genus by Aurivillius ia 1892 and 1893 were so provided. The species 

 to which Dr Willey's specimens are referable is distinguished from the others by the 

 circumstance that the occludent margin of the terga does not reach the orifice of 

 the capitulum, so that the apex of the latter is uncalcified. Also the basal edge of 

 the scuta is more emarginate than in other species. 



Length, of the largest .specimen, 12'5 mm., by a breadth of 6'25 mm, with the 

 wrinkled peduncle constituting 2-o mm. of the total length, but absolutely a little 

 longer by reason of interlapping. Aurivillius speaks of the peduncle as § of length 

 of capitulum, but gives total length 12 mm., capitulum 7 mm., peduncle 4 mm., and 

 further says that ' the peduncle is short and thick,' and figures it in the proportion 

 of 2 : 5. As a matter of fact the proportions vary considerably in the spirit specimens, 

 but whether Aurivillius intended to convey that idea I cannot say. 



