MUSEUM OF COMPARATIVE ZOOLOGY. 455 



No. 5. — Appendix to the Preliminary Report (Bulletin No. 9, 

 Yol. I.) on the Echini collected by L. F. de Pourtales. By 

 Alexander Agassiz. 



The two species of sea-urchins here briefly noticed are interesting 

 in a geographical point of view ; the one being a second species of a 

 genus thus far only known from the Indian Ocean ; the other as 

 additional evidence on an interesting question of geographical distribu- 

 tion in the Atlantic Ocean. 



Among the Echini collected by Mr. Pourtales in 1868-69, during 

 his exploration of the Gulf Stream, were numerous fragments of spines 

 of sea-urchins which I was unable, at the time of writing the prelimi- 

 nary report, to refer to any genus of Echini known to me. Having 

 while in Paris had the opportunity — thanks to Professor Bayle — of 

 examining Michelin's collection now in the Ecole des Mines, containing 

 among other types a remarkable sea-urchin of which only a single 

 specimen exists, described by Michelin, in Annexe A to Maillard's 

 notes sur l'isle de Bourbon, in 1863. 



This sea-urchin he named Keraiaphorus Maillardi ; it was brought 

 up from a depth of two hundred metres on a fishing-line, and was 

 called Keraiaphorus on account of its long curved spines, resembling 

 the antennas of Cerambycidcz. The fragments of spines collected by 

 Mr. Pourtales off Tennessee Reef, at a depth of one hundred and sixty 

 fathoms, belong to this genus, but differ sufficiently in appearance to show 

 they do not belong to the same species. They are of a bright vermilion 

 on the concave part of the spine, and a light pink on the opposite side ; 

 the extremity of the spine is white for a considerable distance ; the spine 

 is slightly curved from the base ; a section of the spines shows them 

 to be somewhat triangular, with rounded sides, the long convex side of 

 the triangle being placed on the side of greatest diameter of curvature 

 of the spine, and the short slightly concave or straight sides on the con- 

 cave part of the spine. The spine is nearly solid, with the exce ption of 

 a small annular space, nearer the centre than the periphery, made up of 

 one row of large triangular limestone cells, such as are so characteristic 

 of spines of Echini ; the central part and the periphery of the spine 

 consist of very minute circular cells closely packed together, present- 



