OP ARTS AND SCIENCES. 193 



comparison with a more extensive series of younger stages. Fortu- 

 nately there are quite a number of the young of Paleopneustes in the 

 Blake collections. 



In Cystechinus there are three species : C. Wyvillii, A. Ag., and 

 C clypeatus, A. Ag., the test of which is quite stout, while in G. vesica, 

 A. Ag., the test is reduced to a mere film, so that even in alcohol 

 the shape of this Sea-urchin reminds one of the crown of an old felt 

 hat which has seen its best days. 



The test of all the Pourtalesi^: is quite delicate, the amount of 

 limestone being, at the great depths where they occur, reduced to a 

 minimum, and yet at the greatest depth at which these delicate Echini 

 are found they are associated with Ophiurans which are by no means 

 wanting in limestone. 



Among the Euspatangina, Spatangus purpureus occurs in the 

 tropics at a depth of 400 fathoms, and Echinocardium australe is 

 found littoral and at the great depth of 2,675 fathoms. With the 

 exception of a new Spatangoid allied to Maretia, Argopatagus vitreus, 

 A. Ag., nothing demanding special notice was obtained. 



Among the Brissina two species of Hemiaster allied to the creta- 

 ceous H. prunella were obtained (H. gibbosus, A. Ag., and H. 

 zonatus, A. Ag.) ; also an extensive series of Hemiaster cavernosus, 

 A. Ag., plainly showing that the several species thus far recognized, 

 H. antarctica, H. Philippii, and H. cordatus, are only the different 

 stages of growth of the males and females of Philippi's original 

 T. cavernosus. In addition to Periaster limicola, A. Ag., which is inad- 

 vertently described from the Echini of the first Blake expedition, a 

 new species of Rhinobrissus (R. hemiasteroides, A. Ag.) and two new 

 species of Schizaster (S. claudicans, A. Ag., and S. japo?iicus, A. Ag.) 

 close the list of this extraordinary collection. 



I can give no better idea of the value of this collection than by 

 stating that there are in the accompanying list not less than forty-four 

 new species. At the time the " Revision of the Echini " was pub- 

 lished, which included the large number of unknown forms collected 

 by Mr. Pourtales in the Straits of Florida, there were not many more 

 than two hundred species of Echini known, and since that time less 

 than fifty species have been added to the list. 



With regard to the geographical distribution of the deep-water 

 species, the North Atlantic is in striking contrast with the North 

 Pacific and the Southern Ocean. The Pacific is remarkable for its 

 numerous species of littoral Cidaridae, which are few in number in 

 the Atlantic ; of Dorocidaris and of Porocidaris, there is one Atlantic 

 vol. xiv. (n. s. vj.) 13 



