228 M. A. Pomel on the Classification of Echinida. 



less types. Some have the anus far from the apex ; the 

 peristome is small and but slightly angular in Echinoconus ; 

 it is large and strongly notched in Pygaster ; others have the 

 frame of the periprocta partly constituted by the genital circle — 

 Echinoclypus ; and as the peristome is strongly notched, there 

 is a manifest passage to the type of the regular Echinida. 



The Globiform Echinida are very homogeneous, but yet 

 they can be divided into two distinct subfamilies, the Cida- 

 rida^ with the ambulacra prolonged on the buccal membrane, 

 and destitute of buccal branchias, and the Echinida^ with the 

 ambulacra not prolonged, but provided with buccal branchiae, 

 applied against the frame of the peristome in a more or less 

 deep notch. 



The Cidarides are only varied in a slight degi'ee ; some 

 have the ambulacra flexuous — Temnocidaris and Gidaris, 

 Others have the ambulacra straight, and the tubercles rela- 

 tively small — Orthocidaris and Diplocidaris. 



The Echinides are, of all the Echinida, those in which the 

 serial arrangement is most difficult to find. We have decided 

 to make two groups of them, the perforation of the mamilla 

 of the tubercles being characteristic of the Diademia and 

 wanting in the Echinia, 



The Salenia have been raised into a tribe, and even into 

 a family, because one of the pieces which, in the ordinary 

 Echinida invest the anal membrane, is in this case fixed to 

 the test, and also because the anus is eccentric in the peri- 

 proctal frame, as is the case in many other Kving types. It 

 is therefore probable that this tribe will be suppressed, or 

 perhaps be distributed among the others. 



The Diademia include several types ; Heterocidarisj with 

 short ambulacral lips and a small peristome ; Hemicidaris^ 

 with a large, diagonal peristome, and with very narrow am- 

 bulacra ; Diadema differing from these by its tubercles being 

 equal in the two areas ; and Pedina with a small peristome, 

 much notched, and with slightly developed tubercles. 



The Echinia are a little more varied; the peristome has 

 its lips but slightly unequal, and its notches sharp in 

 some; the test has no sculpture, and the tubercles of the two 

 areas are unequal in ^ropeltis^ subequal in Phyma^oma and 

 Coeloplewrus ; the test is ornamented with sculpture and im- 

 pressions in TemnopleuTus and Salmacis, The peristome has 

 no notches, or very slight ones, and the lips are very unequal 

 in CodechinuSj equal in Psammechinus. Its notches are very 

 clean, and even deep, and the lips very unequal, in Magnosia 

 and Stomechinus. The peristome is almost round, and the 

 notches are narrow and deep in Tripneustes. Lastly, with 



