426 Rev. M. J. Berkeley on Ditrupa and Filogranda. 
animal of which indeed I have seen only a single specimen ; but this was 
enough to prove it most clearly congeneric with Dentalium subulatum, 
though from the complete evaporation of the spirit in which it was pre- 
served and the circumstance of the surface of the operculum being over- 
grown with Ceramium repens and another minute Alg@, I was not able 
to understand its strueture sufficiently to give a figure. I at first thought 
that there were some appendages to the operculum: nor from the 
extreme minuteness could I ascertain so certainly the nature of a third 
substance, in.addition to the two .4/ye¢ above mentioned, as to pronounce 
decidedly upon the point with such scanty materials. It is highly pro- 
bable that the other minute British Dentalia will prove to possess an 
animal of like structure, though possibly even in that case it would be 
requisite to place them in a distinct genus. 
The characters of the genus 
DITRUPA 
are as follows. 
Shell free, tubular, open at both ends. 
Operculum fixed to a conical pedicellated cartilaginous body, thin, 
testaceous, concentrically striate. 
Branchie 22 in two sets, not rolled up spirally, flat, broadest at the 
base, feathered with a single row of cilia. 
Mantle rounded behind, slightly crisped, denticulated in front, strongly 
puckered on either side. 
Fascicles of bristles 6 on each side. 
I take this opportunity of referring to the two Serpule described in 
Vol. 3, p. 229. Since the account there given was published I have 
dredged several specimens of Serpula Arundo*, and find my former 
observations confirmed. It belongs to the genus Sabella as characterised 
* Serpula Arundo, Turton, Serp. tubularia, Mont. The latter name being 
the original ought to be retained, and the species named Sabella tubularia. 
Serpula tubularia, Turt. is quite a different species, and the same with Serp. 
vermicularis, Lam., excluding var. b, I am obliged to Dr. Johnston for calling 
my attention to this point in Loudon’s Magazine of Natural History, vol. 7, 
p. 126, 
