REPORT ON THE CRUSTACEA MACRURA. 53 



mastigobranchia, and the pleurobrancliia, which is well developed, is implanted high upon 

 the pleura, and is directed anteriorly, lying nearly horizontally beneath the carapace. 



In the three next anterior pairs of appendages the pleurobrancliia is implanted much 

 lower, and traverses the .same line as the overlying podobranchia. The first pair of 

 pereiopoda has no pleurobrancliia, nor has the second pair of gnathopoda, while the first 

 pair (PI. VII. fig. 1, h) has no branchial plume whatever, and the mastigobranchia is 

 reduced to a rudimentary stump, fringed with a thick brush of hair. 



The third pair of siagnopoda (PL VII. fig. 1, g) supports a broad and tolerably long 

 mastigobranchia, to which is attached, on the upper margin near the base, a small styliform 

 process, fringed with ciliated hairs on one side and simple ones on the other. This organ 

 I take to be the rudimentary homologue of a podobranchial plume. On the second pair 

 of siagnopoda the mastigobranchia is also present, and is large, broad, and rounded at 

 the apex ; the margin fringed with short posteriorly-directed plumes or hairs. 



The entire branchial apparatus corresponds very closely with that of Phoberus, and 

 resembles in general structure that of the Palinuridas. 



Observations. — Thaumastocheles zaleuca is a blind species, and most probably fossorial 

 in its habits. That it is a degraded form I think we may safely infer from the excavations 

 which correspond with the orbits still remaining in the anterior margin of the carapace, 

 as well as from the depressions in the first pair of antennas, such as exist in those specimens 

 in which the ophthalmopoda are well-developed. 



The metope is a smooth perpendicular plate, bearing two small tubercles tipped with 

 a small brush of hair that projects from the surface immediately on each side of the 

 median line. The general appearance of the metope is sub-membranous and translucent, 

 and it is highly probable that the optic nerve terminates so closely behind it as to 

 receive impressions of light, although probably of a very subdued character, as in 

 the subterranean Amphipoda. The assumption that there is consciousness of light 

 appears to receive support from the extent of surface which the metope occupies 

 (PL VI., c"), and the depressed position of the first pair of antennas. 



The first pair of antennas lies inside the second pair and in the same line with it ; the 

 upper surface is excavated as if it had been so formed to admit of the presence of a large 

 pedunculated eye, which has disappeared. At the lower part of the metope and just 

 above the attachment of the first pair of antennas the small, fixed, rounded and polished 

 tubercles, very close to but not associated with the articulation of the antennas, may be 

 the remains of the peduncle of the obsolete eye ; but this is only suggested, because I do 

 not remember to have observed similar tubercles in any form of Crustacea where the 

 ophthalmopoda are developed. 



The idea of this species being more or less fossorial in character is suggested by 

 several anatomical conditions : the bhndness of the animal; the operculum at the anterior 

 passage of the branchial chamber ; the strong pleocleis on the first somite of the pleon, 



