S. I. Smith — Crustaceans of the Atlantic Coast. 
81 
cimens examined, all the males 28 mm or less in length have well-devel- 
oped rostral teeth and a distinct spine (the pterygostomian) at the 
inferior angle of the anterior margin of the carapax, and in these 
characters agree fully with the female. In all the specimens much 
above 30 mm in length the pterygostomian spines are small, rudiment- 
ary or wanting, though they do not seem to disappear wholly at any 
particular size of the individual. The disappearance of the dorsal 
teeth of the rostrum is still more irregular and is evidently a charac- 
ter peculiar to, but not characteristic of, the adult male. There are 
often very rudimentary teeth present which could not be discovered 
without the aid of a lense, and the gradation between the forms in 
which they are well-developed and those in which they are wholly 
wanting is most complete. That the form of male with edentulous 
rostrum and without pterygostomian spines has no claim to be 
retained as a species is conclusively shown, (1) by the complete gra- 
dation in these characters between this form and the original polaris- 
forrn, (2) by the fact that one of the characters may exist without 
the other in the same individual, and (3) by the negative evidence 
that there is no corresponding female form. 
The following tabulation of the character of the rostral teeth and 
the pterygostomian spines, together with the length of the individual 
and the rostral formula, in a series of specimens selected from a much 
greater number, exhibits some of the variations. The letters indicat- 
ing the localities correspond with those in brackets under the distri- 
bution of the species given above. 
Locality. Sex. 
Length. 
Rostral 
Formula. 
Dorsal teeth 
of rostrum. 
Pterygostomian spine 
k, 
23-7mm 
2 + 3 
Well-developed. 
Well-developed. 
k, 
240 
2 + 2 
tl 
ii 
k . 1 
250 
2 
2 + 3 
ii 
U 
l. “ 
25-7 
3 
2 4**i 
a 
u 
/, 
200 
2~ 
2 + 5 
3 
- 
“ 
c, '• 
26-5 
2 + 4 
2 
“ 
“ 
/, 
27 0 
2 + 5 
.1 
b, “ 
280 
4 
2 + 2 
2 
« 
A-, “ 
20-0 
2+3 
3 
“ 
“ 
c, “ 
320 
2 + 2 
it 
Small. 
:t 
Trans. Cons. Acad., Vol. V. II 
Kkbhiary, 1 »7U 
