MUSTELUS MEGALOPTERUS. 
DIMENSIONS. 
Feet. Inches. Lines. 
Length from nose to apex of caudal 
fin 4 9 0 
Circumference immediately before 
first dorsal fin 1 5 0 
Distance between nose and eye ... 0 3 0 
Distance between nose and angle of 
mouth 0 3 6 
Distance between nose and nostrils 0 10 
Distance between nose and middle 
of upper jaw 0 2 9 
Breadth between the angles of the 
mouth 0 4 0 
Distance between eye and post 
ocular spiracle 0 0 4 
Distance between eye and first 
branchial opening 0 4 0 
Distance between nose and anterior 
edge of first dorsal fin 0 17 6 
Feet. Inches. Lines 
Distance between hinder-edge of 
first dorsal and anterior edge 
of second dorsal 0 12 9 
Distance between base of second 
dorsal behind, and base of 
caudal fin 0 5 0 
Distance between nose and an- 
terior edge of pectoral fins 0 10 0 
Distance between base of pectoral 
fin beliind, and anterior edge 
of ventrals 0 13 9 
Distance between base of ventrals 
behind, and anterior edge of 
anal fin 0 8 0 
Distance between posterior edge 
of anal behind, and base of 
caudal fin 0 4 0 
Length of anal appendages 0 6 6 
The chief external differences between the male and female consist in the 
latter wanting the anal appendages, and haying the fins, particularly the 
pectoral ones, proportion ably smaller. 
In the course of several years during which the fishermen of Cape Town were engaged by 
me in collecting cartilaginous fishes, only a very few specimens of this species were obtained. 
Their want of success, however, probably arose more from the species resorting to situations 
little visited by fishermen during their ordinary avocations, than from the scarcity of specimens. 
It feeds upon mvllusca, Crustacea, 6fc., and in quest of these it haunts principally the rocky, or 
broken parts of the coast. 
Specimens of this species are occasionally procured, in which the ground colour, similar to 
that described, is freely spotted with dusky black blotches, very various as to size. 
As I have not had an opportunity of ascertaining whether the males of the species of this 
genius are provided with sacs, similar to those which occur in several of the other genera of the 
Squalidce, and which sacs appear to be connected with the anal appendages, I would suggest 
the inquiry, as deserving the attention of those naturalists who have an opportunity of ex- 
amining specimens of the European species. The sacs to which I allude, two in number, lie 
under the skin of the abdomen, immediately in front of the anus, are of a pyriform shape, and 
each, by means of a narrow duct, opens into the longitudinal groove, which exists on the inner 
side of each anal appendage. In none of the sacs which I examined was I able to detect 
any fluid beyond what was barely sufficient to lubricate their inner surfaces, and from whence it 
proceeded I could not discover; no glandular structure was noticed. Farther enquiries, I have 
no doubt, will shew them to be essential to the proper performance of the functions belonging 
to the appendages; and as tending to give probability to that supposition, I may merely 
observe that by injecting water into one of these sacs, the corresponding appendage was dis- 
tended to a great size, and its apex expanded, flattened, and rendered well adapted for fixing 
upon, or seizing extraneous bodies. 
