52 Natural History Bulletin. 



This is Crxftofodia concaza Stimpson, having a triangular 

 carapace so concave on the dorsal surface as to resemble a bit 

 of shell, but with three prominent ridges meeting at a point 

 near the anterior margin of the carapace. The chela is long 

 and trigonal. When its various appendages are retracted, 

 only the closest inspection discloses the fact that this animal is 

 a crab at all, the real dorsal surface resembling the concave 

 surface of a piece of shell, a deception still further enhanced 

 by its color, which is whitish. 



Among the macroura the only one which we will notice 

 was an Alfheiis. which occurred in great numbers in the 

 various water channels of the massive sponges. They were 

 pale brown in color, and like others of the genus were charac- 

 terized by the enormous chela, which is longer and heavier 

 than all the rest of the animal. A number of specimens of 

 this species were placed together in a glass jar. and every once 

 in a while a noise was heard resembling more than an}thing 

 else the cracking of thin glass under the pressure of freezing 

 water. The animals were taken out and placed in a tin dish, 

 but the noise still continued. Careful observation disclosed 

 the fact that this peculiar noise was made by the snapping 

 together of the two lingers of the great chela. How this par- 

 ticular sound could be produced by a substance so compara- 

 tively soft as these organs, is a mystery. This species seems 

 to be on the road to losing its eyes, these organs being com- 

 pletely overgrown by the rostrum, which seems to actually 

 press upon the upper surface of the eyes. 



The above are onh' a few of the interesting Crustacea 

 secured on the Great Bahama Banks, but they serve to show 

 what a delightful experience our naturalists enjoyed at this 

 time. About twenty-eight species of mollusca were collected 

 while we were at work on the Banks, among which were 

 interesting species of Avicula. Astralinni, Ccrithiiini and 

 Trivia. The most conspicuous Echinoderm was Pcntaccros 

 rcticulatus, of which enormous specimens were secured, some 

 being too large to go into the collecting tubs. The dried 

 specimens of this star-fish usually seen in museums do not con- 



