THE SESSILE BARNACLES. 221 



B. auricom-ft Hock. 



B. cUiatus IToek. 



B. campressus Hoek. 



' Before proceed ing with the descriptions of species, I may be per- 

 mitted some remarks on Balanus a-ncas Lanchester, 1 of which I have 

 been able to examine the type material, through the courtesy of 

 Mr. C. Forster Cooper, in charge of the University Museum of 

 Zoology, Cambridge. 



The type as preserved consists of both scuta and terga of one indi- 

 vidual (pi. 47, figs. 2, 2(7, 2<7, 2f/) and a scutum and tergum (pi. 47, 

 fig. 2Z>) of another. I have therefore not been able to add any- 

 thing to Mr. Lanchester's account of the walls, basis, or internal 

 anatomy. 



The scutum has narrow, very little raised and widely spaced 

 growth ridges, much like some forms of B. amphitritc. The articular 

 ridge is prominent and somewhat reflexed. The adductor ridge is 

 very narrow and low, and there is a smaller ridge parallel with it, 

 nearer the articular rib; these two ridges are connected above by a 

 semicircular ledge, bounding the flat, depressed interval between 

 them; and in suitable light they appear to form a narrow inverted 

 U. The pit for the lateral depressor muscle is small but distinct. 

 The tergum has a distinct though quite shallow depression running 

 to the spur, varying in depth in the two individuals. The carinal 

 margin is arched, and shorter in one of the examples, and it bears 

 numerous delicate hairs. The crests are well developed. 



It will be noted from the above details, together with Mr. Lan- 

 chester's account, that this form agrees veiy closely with B alarms 

 social* s Hoek. 2 I can find no tangible differences; and unless the 

 cirri (which are not described in B. a'neas} are shown to differ, I 

 would suggest that B. ceneas be written as a synonym of B. socialis. 



I may further remark that B. socialis and B. ceneas differ from the 

 other forms of frolldobalanus by having very narrow, smooth radii, 

 with steeply oblique summits, whereas the other species have wide, 

 transversely grooved radii, with summits far less oblique; yet from 

 Doctor Hoek's account of the mouth parts of B. socialis, it appears 

 to belong with the other Solidobalani rather than with the B. ama- 

 ri/ttis group. 



(r/iff/.s Lanchester, Proc. Zool. Soc., London, 1902, vol. 2, p. 370, pi. 34, 

 figs. 4, 46. Malay Peninsula, on the shells of Strombus and Natica inhabited by the 

 hermit crab Pacninif; JirsKii Miers (Proc. Zool. Soc., London, 1902, vol. 2, p. 3641. Col- 

 lected by the Skeat expedition. 



" Balanus socialis Hoek, rjiallenr/er Report, Zoology, vol. 8, Report on the Cirripedia, 

 p. 150. pi. 13, figs. 23-28 (1883). Si&o^a-Expeditie, Cirripedia, p. 192, pi. 18, figs. 2-12 

 (1913). Arafura Sea, type locality; also Malay Archipelago, in 9 to more than 69 meters. 



