176 THE VOYAGE OF H.M.S. CHALLENGER. 



The rhipidura is symmetrical, with broad and disc-shaped, foliaceous plates, the outer 

 of which is marked with a diseresis. 



This genus w T as first established to receive a species, Nephropsis steioarti, dredged by- 

 Mr. Wood-Mason, which that author, in the above work, as well as in the Ann. and Mag. 

 Nat. Hist. (vol. xii. p. 60), described as the typical species, and was taken 25 miles off 

 Ross Island, on the eastern coast of the Andamans. He says " That the specimen was 

 really brought up from this great depth (260 to 300 fathoms) is certain from the unmis- 

 takable signs of crushing from contact with the lip of the dredge, from its position in the 

 dredge-bag, and from its firmly adhering greenish coat, which appears to indicate that, 

 like Calocaris rhacandrese, it is a burrower." 



Mr. Wood-Mason further adds that, "The discovery in these warm seas of a very near, 

 the nearest ally, in fact, of so characteristic a cold-water species, remarkable though it is, 

 will not appear so surprising when I mention that my Crustacean lived and burrowed in 

 the mud of the sea-bed at a depth of nearly 300 fathoms, in a temperature certainly not 

 exceeding 50° Fahr." 



The Challenger's specimen was taken at a depth of 800 fathoms, a few leagues south 

 of New Guinea, at a temperature of 39°"5, which represents some 10°'5 of temperature 

 still lower. 



The same naturalist further remarks that "One of the chief points of interest attaching 

 to this new form lies in the loss of its organs of vision by disuse, as in Calocaris macan- 

 drew, Bell, in Cambarus pellucidus (a member of the same family as that to which 

 Nephropsis belongs), and in the other Crustaceans and animals inhabiting the caves of 

 Carniola and Kentucky. I not only agree with Mr. Darwin in attributing the loss of 

 the eyes to disuse, but I also regard the great length and delicacy of the antennae, and 

 the great development of the auditory organs, as modifications effected by natural 

 selection." 



It appears, both from Wood-Mason's own figures and from an examination of the 

 Challenger specimens, that this genus cannot be described as being without organs of 

 vision. That the ophthalmus does not occupy a greater space than the diameter 

 of the peduncle, and the absence of the dark pigment that generally gives colour 

 to the eye may be evidences of degradation ; but I have little doubt that the 

 power of vision is equal to the animal's requirement. The ophthalmopoda are slender, 

 but in Mr. Wood-Mason's figure they are about one-fourth the length of the rostrum, 

 that is, equal to the average length. In Calocaris macandrese, to which he compares his 

 species, the peduncle seems wanting, but the ophthalmus is figured by Bell as being 

 quite equal in diameter to the eyes of simdarly proportioned Crustacea, but the absence 

 of colour prevents our readily detecting the form of the organ. In the genus Alpheus 

 the peduncle of the eye is often shorter than in either Calocaris or Nephropsis, but 

 since the organ is lined with black pigment no one would think of describing it as 



