GENERA A'ND (GROUPS OP THE ECHINOIDEA. 143 



it is certain from the construction of the ambulacra, the nature of 

 the periguathic processes, the development of the internal sup- 

 ports of the tests, aud the formation of the apical systems, that 

 there is more than a subfamily distinction to be made between 

 these groups. Again, Lagamtm is the type of a subfamily (Laga- 

 nid^e, A. Agass.) of the same family Euclypeastridae, but it de- 

 parts extremely from the Fihularma and the Echinanthus of A. 

 Agassiz. The Scutellidae, the secoud family, hare no subfamilies 

 in the classification of A. Agassiz, yet AracJinoides and Botula 

 find a place in it as genera. It appears that the subfamily is 

 made too prominent and at the expense of limiting the family 

 in this classification. 



After due consideration it appears that the types of the Cly- 

 peastridse, mentioned above, should be representatives of families, 

 and that the entire group is worthy of the same classificatory 

 value and position as the Endocyclica with jaws. Clans may be 

 taken as a writer having much experience, and in his ' Zoologie ' 

 he follows tbe method of A. Agassiz, but considers his suborder 

 as an Order of the Class Echinides, the Echinodermata as a 

 whole being a Type of Invertebrata. 



It seems therefore advisable to call the Order — Clypeastroida, 

 and to partly follow Agassiz and A. Agassiz, by establishing the 

 families Fibulariidge, Clypeastridge, and Scutellidse. 



Order IV. CLYPEASTROIDA (p. 25). 



Syn. ClypeastridcB, Agassiz (suborder), 1836. (Enlarged.) 



Test either flat, or tumid, or rising dorsally, witb a thin or tumid 

 margin which may be notched ; the internal floor and roof 

 connected by calcareous pillars and partitions, limiting more or 

 less the internal organs, and forming, or not, false walls as 

 coverings to the water-system. 



The apical system with a central madreporite ; basal plates 

 coalesced. 



Ambulacra more or less polyporous ; tentacles heteropodous. 

 Petaloid parts of the ambulacra both with branchial and disci- 

 ferous tentacles in the poriferous zones; usually very numerous 

 simple small tentacles, each one in relation with a single pore, in 

 the interporiferous areas, placed in simple or branching grooves, 

 or along the transverse sutures or in the plates generally ; tubular 

 branchial tentacles at the peristome. 



Interradia smaller than the ambulacra, may be disconnected, 



