PORIFERA OF THE L.M.B.C. DISTRICT. 215 



clwndria suhurea, and says, in regard to its liabitat, " It 

 has the singular property of being attaclied only (so far as 

 1 have been able to ascertain) to old univalve shells, which 

 it entirely invests." He mentions then that most of those 

 shells w^ere inhabited by hermit-crabs. Schmidt's* defini- 

 tion is similar, " Suberites globosus, incrustans et invol- 

 vens conchas, quas Paguri domos sibi elegerunt." Mr. 

 Higgin has already recorded specimens of this peculiar 

 habit from Holyhead and Morecambe Bay, and I am able 

 to add Calf of Man, v^here it w^as dredged on the " Hyaena" 

 expedition of April, 1889. But still this species does not 

 seem to restrict itself exclusively to univalve shells in- 

 habited by hermit-crabs, although those cases are the 

 conspicuous and interesting ones. A sponge, ap[)arently 

 of the same species, was dredged on the above mentioned 

 " Hyasna " expedition of April, 1889, and also off Calf of 

 Man. It encrusted a living Pecten opercularis, forming a 

 thin layer (about 2 mm. in thickness) of greyish colour. 

 I have found it also encrusting tetractinellid sponges, on 

 Seiriola compacta, mihi, and on Stelletta colling si, B. As I 

 shall state more fully on page 221, 1 erroneously described 

 in my former report such an encrusting layer of Suberites 

 domuncula as the ectosome of Seiriola. The upper portion 

 of fig. 1, PI. VIL, Vol. IIP, Proc. Liverpool Biol. Soc. may 

 therefore be taken as a fairly correct representation of 

 a vertical section through a Suherites domuncula. The 

 thickness of that specimen was unusually small, only 

 about 0'24 mm. Tlie spicules of it are tylostyli O'l to 

 0*38 mm. by 0"003 to 0'006 nnn. They are arranged in 

 bundles, and project for about one-half of their length 

 through the ectoderm. The heads of the longer tylostyli 

 are supported by the basal membrane. The figure also 



* Oscar Schmidt, " Spongien des Adriatischen Meeres," Tlieil i., p. 67. 



