182 



BULLETIN : MUSEUM OF COMPAKATIVE ZOOLOGY. 



nearest to the ancestral form and the centre from which the different 

 genera have come. Whether Tylocidaris represents a more primitive 

 type, because of its imperforate tubercles, is an open question. The 

 other genera fall rather naturally into three groups, which correspond 

 to the three " sous-tribus " of Pomel, but the lines between these groups 

 are not clear enough to warrant any recognition of subfamilies. The 

 following table indicates these three groups, and in the succeeding pages 

 the genera will be taken up in the order here given, which indicates 

 roughly their possible relationships. 



Phyllacanthus. 



Chondrocidaris. 



Diplocidaris. 



Tetraciuaris. 



Stephanocidaris. 



Teumocidaris. 



Tylocidaris. 



Cidaris. 



Goiiiocidaris. 



Polycidaris. 



Orthocidaris. 



Dorocidaris. 



Tretocidaris. 



Calocidaris. 



Austrocidaris. 



Centrocidaris. 



Aporocidaris. 



Stereocidaris. 



Anomocidaris. 



Acautliocidaris. 



Porocidaris. 



Diagnoses of the Genera, and the Recent Species. 



In view of the large number of recent Cidaridae described since the 

 publication of A. Agassiz's " Challenger " Echini, a complete revision 

 of the family will not be without value, so, to the extended diagnoses of 

 the genera here accepted, artificial keys to the recent species contained 

 in each are added, with a few remarks concerning each one, and a refer- 

 ence to a good figure when one has been published. Three apparently 

 new species, represented in the Museum of Comparative Zoology by 

 several specimens each, are also described and figured. No attempt at a 

 synonymy is made, since the " Revision of the Echini " gives all that is 

 needed in that line for the species long enough known to have been 

 burdened with many names. References to published figures are given 

 for every species which has ever been figured, and photographs are 

 added of all species which have never been figured hitherto, except only 

 Dorocidaris nuda, of which no specimen has been available. 



