272 



successive beds of the neocomian. He showed the relation of 

 these to other echinoderms, and the gradations in the various 

 orders. Of the four orders, crinoids, starfishes, echini, and 

 holothurians, the first is synthetic, combining some features of the 

 higher orders, yet on the whole inferior to them ; this is the ear- 

 liest and prophetic type, and is found from the Potsdam sand- 

 stone up to the present time, from the cretaceous upward mostly 

 free. Starfishes and echini begin with the Triassic period, and 

 are numerous now ; the crinoids of the Permian and carbonifer- 

 ous have affinities with the echinoids and starfishes ; from their 

 structure these are perishable, and hard to preserve in a fossil 

 state, — the echini being the best preserved ; the slender-armed 

 ophiuroid genera are the oldest. Echini increase as crinoids di- 

 minish, arriving at their maximum in the cretaceous, and from 

 that becoming less numerous ; only two are found here, on the 

 coast of South Carolina half a dozen, on that of Florida more 

 than twelve, and not more than two dozen would be found in the 

 most favorable localities under the tropics ; fifteen species might 

 be considered a fair representative of a fauna, and that number 

 are found in subdivisions of the Jurassic and cretaceous ; and 

 these, therefore, may be adduced as evidence of the distinctness 

 of the faunte. The echini as an order present four types or sub- 

 orders : 1st, Echinus proper, with the mouth central below and 

 the anus central above, with such types as Cidaris, Diadema, 

 Echinus, Echinometra, &c. ; 2d, Echinolampas, with no teeth ; 

 3d, Clypeaster ; and 4th, Spatangus. No holothurian has as yet 

 been found fossil, and, if not exclusively belonging to the present 

 epoch, they probably did not antedate the Tertiary period. All 

 echini found in the Trias, Lias, Oolite, and Jurassic belong to the 

 1st sub-order, the 2d and 4th coming in during the cretaceous 

 period ; the older forms have the more simj^le ambulacra ; the 

 earliest spatangoids have no connecting groove between the pores, 

 in this respect resembling echinoids, but the later ones present 

 this groove ; the specimens exhibited had such echinoid affinities. 

 The relation between these sub-orders and their types is unmis- 

 takable, showing something more than derivation, and indicating 

 a system or plan. Thanks to Johannes Muller, the embryology 

 of the four sub-orders of echini is well known ; the young Echini, 

 &c., are like the adult Cidaris ; so the young Echinolampas, 



