BIHAXG TILL K. SV. TET.-AKAD. HAXDL. BA>-D 18. AFD. IT. X:0 1. 55 



Meanwhile it seems allowable to expect that tlie modifica- 

 tions of these parts in the G-alerites will be found to be de- 

 viations from the type of tbe Regiilaria to wliich the Echi- 

 noconidse are allied in other respects. They are regular. the 

 mouth being central and the cah^x right över it; their ani- 

 bulacral plates compound in the same manuer, and they had 

 extemal gills. The position of the excretory opening is of 

 bnt seeondary importance. 



The earliest acconnt of the dental system of the Clypea- 

 stridse is found in the work of Klein. • and. after him, in that 

 of Parra- a good description qnoted by Desmouldts and Jo- 

 HANXE? XuLLER. Some particnlars relating to the Clypeaster 

 Eangianus were added by Desmouldcs.^ Joha^-^es MItleb,'* 

 who showed that in this group the same principal parts are 

 present as in the Regularia. five pyramids, ten epiphyses and 

 tive rotulse. bnt that the compasses are absent. described and 

 figured with great care the whole apparatns in Ch-peaster, 

 Arachnoides and Mellita. AleX-A.nder Agassiz^ represented it 

 in Clypeaster hnmilis , Cl. reticulatus L.. and Lobophora 

 aurita Leske. 



The dental system of Clypeaster reticulatus L.. PJ. VIL 

 firj, 52—62. Fl. VIII, fig. 65—72. Pl XI. fig. 144. when com- 

 pared with that of the Regularia, for instance that of Echino- 

 metra Lucunter L.. Ph VII. fig. 63. 64, presents not a few 

 distinctive features. In the Echinometra its greatest dimen- 

 sion is the vertical. in the Clypeaster the horizontal. In the 

 former the whole of the five concentrically arranged. uniform 

 and equal pyramids constitutes a regular inverted cone, the 

 horizontal section of which is circiUar; in the Clypeaster it 

 forms an elevated pentagonal står, the sides of which, slightly 

 reentering, are miequal. fig. 144. K the largest side. the 5, is 

 taken = 1, the 2 and 3 are each = O, se. and the 1 and 4. of 

 greater reentering depth. each = 0,6 7. In the Echinometra 

 the alveoles are teudincr to close interiorlv, the wings being 



' Dispositio. p. 43. t. XXXIH. fig. li— s 



- Desoripcion de liifferentes piezas de Historia Xatnral. Havanna 1787. 

 p. 137. Pl. 02. fig. 1—10. 



3 Etudes. p. (3G, 185. Pl. II. 



* Ueber den Bau d. EcMnodermen, p. 74, pl. VLl fig. 13-16. Berl. Ab- 

 handl. 1851. 



» Revision, p. 688, Pl. XI a. XXVni. XXX fig. 1. 



