296 BULLETIN OF THE 



have said of the Galeritt - with teeth, I should be inclined to add them 

 to the suborder as one of its three subdivisions, which, as here limited, 

 are the Cidarida3, the Echinidae proper, and the Galerites. The sub- 

 order of "irregular" Echini, after the withdrawal of the Galerites, still 

 contains the Clypeastroids. From the structure of the ambulacral system, 

 they have some affinity with the Spatangoids ; yet the presence of par- 

 titions and teeth, combined with petaloid ambulacra, seem to con- 

 stitute good subordinal characters for the Clypeastroids as contrasted 

 with the Spatangoids proper, which include all edentate forms, taking 

 in also the edentate genera formerly placed among Galerites as well as 

 the Cassidulidae, sometimes regarded as independent suborders. 



III. Baihymetrical and Geographical Distribution. 



The accompanying table (pp. 208 and 299) shows at a glance the 

 principal features of distribution of the different zones of depth. We 

 can distinguish a strictly littoral fauna, extending from tide-mark to gen- 

 erally less than 10 fathoms, though a few of the species characteristic of 

 this zone extend to a depth of 34 and 40 fathoms. This fauna consists of 



Diadema an till arum. 

 Echinometra Michelini. 



" viridis. 



Lytechinus variegatus. 

 Tripneustes ventricosus. 

 Clypeaster rosaceus. 

 Stolonoclypus Ravenellii. 

 Mellita testudinata. 

 Encope Michelini. 



" emarginata. 

 Echinoneus semilunaris. 

 Brissus columbaris. 



A second set (if specie-. less numerous, extends from the shore to a 

 much greater depth, — from <so to about 120 fathoms. They are 



Cidaris annulata. 

 Echinocidaris punctulata. 

 Meoma ventricosa. 

 Plagionotus pectoralis. 

 Mccra atropos. 



