48 PROF. P. M. DUNCAN AND AIR. W. P. S LADEN ON THE 
In naming these latter creatures specifically, I have done so 
with considerable hesitation, as it must be confessed my know- 
ledge of these groups is much too limited to warrant my speaking 
with any great degree of certaiuty. 
Thus ends my notes on Dumpenus lampetriformis ; and I trust 
its habits and history have not been left shrouded altogether in 
the darkness in which I found them. 
Since writing the foregoing I got, on June 5th, five more 
specimens of Dumpenus , one of them, a female, carrying spawn, 
which would have been deposited within a fortnight or three 
weeks at latest. This brings my supposition relative to the 
time of spawning to be pretty nearly correct, viz. the end of July 
or beginning of August. 
The longest specimen mentioned by Collett was 412 millim. ; 
my longest one was 121 inches. 
On the Anatomy of the Perignatliic Girdle and of other Parts 
of the Test of Discoiclea cylindrical Lamarck, sp. By Prof. 
P. Martin Duncan, F.B.S., and W. Percy Sladen, P.G.S., 
Sec. L.S. 
[Read 17th June, 1886.] 
Discoidea cylindbica , the Galerites cylindricus of Lamarck, is 
one of the commonest of the Echinoidea from the Upper Creta- 
ceous strata ; and its shape and internal casts in flint are familiar 
to all geologists. Desor, Wright, and Cotteau have described 
the species; and the last-named palaeontologist has enlarged the 
generic diagnosis of Discoidea in consequence of some morpho- 
logical details which had been elaborated by himself and some 
previous observers, especially E. Eorbes and Loven. 
Discoidea cylindrica has five basal plates in its apical system, 
and the fifth or the posterior one is not perforated for a genital 
duct. But the palaeontologists just mentioned found a perforated 
fifth basal in species which they felt bound to classify in the 
genus Discoidea. Loven, speculating on this association of im- 
perforate and perforate basals in different species of the same 
genus, considered it an instance of evolution during time. 
Cotteau extended the generic diagnosis, and added to that of 
Desor the following : — “Apical system compact, subpentagonal, 
