360 MR. ALDER ON ADDITIONS TO THE MOLLUSCA 
and is obscurely striated spirally. Aperture roundish 
ovate, a little produced and subangulated at the base , 
outer lip thin, faintly crenulated inside ; inner lip with a 
strong tooth, placed centrally, and a narrow umbilicus 
behind it. Length, 3 tenths ofan inch; breadth, 11 tenths. 
This new species of Odostomia is the largest I am acquainted 
with. Its nearest ally among described species is the Odostomia 
unidentata, from which it differs in the greater size, the more 
produced spire, and the crenulations inside the lip.* 
One specimen, dead, but tolerably fresh, was obtained from the 
first day’s dredging. I have since found a young individual 
among some small shells dredged off Douglas, Isle of Man, in 
June, 1848. 
OposTomra acuta, Jeff. 
Odostomia acuta, Jeff., in Ann. Nat. Hist., 2nd series, 
v. 2, p. 338. 
This has been described by Mr. Jeffreys since the pub- 
lication of our Catalogue. Two worn shells, found at 
Tynemouth, which I had there mentioned as probably 
distinct from O. wnidentata, Mr. Jeffreys considered to be 
varieties of his species. The acquisition of a few better 
specimens by dredging enables me to say that the shell 
found on this coast will probably prove to be distinct and 
new. It is intermediate between O. wnidentata and O. 
acuta, but the whorls are more rounded and the umbilicus 
much larger than in either species. I should propose for 
it the name of O. wmbilicata. 
Rissoa vitReA, Dont. 
Turbo vitreus, Mont. Test. Brit., 321. 
One specimen of this rare shell occurred. The first 
found on our coast. 
* Since writing the above, I find Mr. Jeffreys has expressed an opinion in 
the Annals of Natural History, that this shell, which I sent him for examina- 
tion, under the name of O. fulva, is a variety of his O. alba, in which opinion 
I can by no means agree. QO. alba is a thin shell with a very small and obscure 
tooth: this is a thick shell with the tooth very large and conspicuous. There 
are other differences, such as general form, size, colour, and striation. Few 
species of the genus appear more distinct from each other than these. 
