ee 



S. LOVEN, ON POURTALESIA, A GENUS OF ECHINOIDEA. 



ing anteriorly a part of the costal irregularly fractured, while expanding it posteri- 

 orly beyond the other costals'). During the next piirioils the poriproct, ahvays placed 

 on the antero-posterior axis and regularly transverse, in Peltastes, which appears in the 





Peltnafes Studeri 

 CoLT. Cretac. 



Pseudosalenia aspera 

 Et. Oolite. 



Goniophorus lunuliitus 

 Ag. Cretac. 





Salenia scntigora 

 Gk. Cretac. 



Acrosalenia spinosa 

 Ag. Ool. 



Acrosalenia angula- 

 ris CoTTA Oolite. 



Acrosalenia patella 

 Des. Cretac. 



Peltastes Valleti 

 Des. Oolite. 



Middle Oolite, affects .slightly and equally the costals 1, 4, 5, and the central disk, 

 while in Pseudosalenia, of the same time, it erodes it deeply, permitting the costal 5 

 to resumé nearly its normal shape. In Goniophorus, of the Middle Cretaceous time, it 

 expands so as to take in great parts of the snrroiindings. In Salenia proper, which raay 

 be followed from early Cretaceous time up to the present period, and in Heterosalenia 

 of the låter Cretaceous, the periproct is for the greater part cut out from the costals 

 1 and 5, and thus, while slightly entering upon the central disk, is drawn över to the 

 right, on the axis 1 — 3, thus conforming to the rule now prevalent in the majority of 

 the Echinida3 and, partly at least, among the Asteriadea, of having the excretory open- 

 ing placed excentrically, to the right of the antero-posterior axis. In view af these 

 marks of a gradual advance, in the Saleniadse, during their geological development, of the 

 periproct, from the hindmost limits of the calycinal system to near its centre, there is 

 some reason for inferring the probable existence, at a remote period, of Exocyclic Sa- 

 lenian forms combining a calycinal system of a nearly intact Crinoidean character with 

 a periproct placed in the interradium of the bivium, perhaps even towards its ventral 

 surface ") 



Be this as it raay, in all the knoAvn Echinidae, the Saleniada3 not excepted, in the 

 earliest forms as in those of the present era, the periproct is endocyclic. In one of 

 the oldest groups, the Cidaridte, the Crinoidean character of the calyx is still strongly 



*) Corapare Acrosalenia miranda Gauthier, Échin. foss. de TAlgérie, II, p. 86, pl. XX, fig. 109, 110. 

 -) The little known Upper Silurian Cystocidaris Zitt. (Echiuocystites Wyv. Th.) is described as having the 

 periproct inlerradial. 



