CENTROSTEPHANUS LONGISPINUS. 411 



Centrostephanus longispinus 



Cidaris (Diadema) longispina PniL., 1845, Wicg. Arch. 



! Centrostephanus longispinus Pet., 1855, Seeig. v. Moss., p. 109. 



The only specimens of this species I have been able to examine were 

 covered with spines, and in this condition the following features may be 

 added to the description of Philippi. The genital plates are somewhat 

 pointed, separated by one or two anal plates ; the ocular plates are small, 

 more or less rectangular. The upper part of the test is bare, both in the 

 ambulacral and interambulacral spaces. 



The pores are arranged in nearly vertical rows, forming arcs of three 

 pairs only near perisome ; actinal cuts very slight. 



Aradas, who is the only one who, since Philippi and Agassiz, has described 

 a specimen of Diadema from the Mediterranean, does not give us any 

 additional information concerning this species ; this is the more requisite, as 

 the West Indian Diadema setosum occurs at Madeira and also in the Medi- 

 terranean. From the external examination it was possible to make of the 

 originals of Agassiz and Philippi, sufficient could be seen of the abactinal 

 system to show its peculiar structure, and also of the buccal membrane, 

 showing the ten large buccal plates carrying small spines so characteristic of 

 Centrostephanus. It is very important that the denuded test should be 

 examined ; the only clew we have of its distinguishing features being the 

 few words of Philippi, in his original description : " C. testa pallide isabel- 

 lina, orbicular!, utrinque valde depressa, ambulacris serie duplici tubercu- 

 loruin munitis ; areis interambulacralibus serie duplici tuberculorum ma- 

 jorum, serieque tuberculorum mediae magnitudinis utrinque inter tubercula 

 majora et ambulacra munitis ; aculeis longissimis, (diametrum testae sesquies 

 aequantibus) violaceo et albido articulatis, longitudinaliter striatis et verti- 

 cillato-aculeatis, verticillis fere aeque altis ac latis ; assulis supremis aculeis 

 majoribus destitutis. Diam. 27'"; Alt. 13'"; Long. max. acuberum 42'"; 

 iam. 4 • 



Philippi mentions the presence of short club-shaped spines, of a bright 

 Vermilion color, on the upper part of the test, on the plates adjoining the 

 abactinal system. These small club-shaped spines are found on all species 

 of the genus, on the newly formed coronal plates, of which there are some- 

 times three to five small plates, formed in rapid succession in the flat part 

 of the abactinal part of test ; in younger specimens these plates remaining 

 of a small size, carry but one minute tubercle, smaller than the smallest 



