226 PALAEONTOLOGY OF ILLINOIS. 



and more modern Echinoids. Pictet, and some others, not only include these 

 ancient forms in the order EcMnoidea, but even view them as forming a section 

 of the family Oidaridae.* Desor also included them in the order, but regarded 

 them as constituting a distinct family, for which he proposed the name Tesseles, 

 and placed them, along with the Cidaridse, aS a suborder "EndocycMques;"^ 

 which arrangement was also followed by Dujardin and Hupe.J McCoy, how- 

 ever, had previously proposed to erect this group into a distinct order, under 

 the name PeriscJioechmidjse, § and Roetner regarded them as constituting a sub- 

 order of the EcMnoidea ;\\ while Prof Agassiz, if we mistake not, thinks the 

 group falls more properly within the Crinoidea. 



Without presuming to undertake the decision of a question upon which such 

 eminent authorities have differed, we must confess that a careful study of an 

 extensive series of excellent specimens of Mclonitcs multipora, with more or less 

 perfect examples of Oligoporus, JPalsechinus, Arcliseocidaris and Lcpidecliinus, 

 compels us to concur with those who regard these types as Echinoids. Although 

 evidently most nearly allied to the Cidaridse, they still seem to present too 

 strongly marked differences to be properly included in the same suborder; and 

 hence we agree with Dr. Roemer in viewing them as constituting a distinct 

 suborder, for which McCoy's name PerisclioecMnidsc may be retained. In a 

 systematic arrangement their position would doubtless be below all the other 

 Echinoids, and next to the Cidaridse, thus forming a distinct suborder from 

 the higher Echinoids. 



The reasons for adopting the conclusions that these forms are true Echinoids 

 and not Crinoids, are, that in the first place, they differ from the Crinoids and 

 agree with a large group of the Echinoids ( Cidaridse) in having an anal and an 

 oral opening, situated at opposite extremities of the vertical axis, with regular 

 ambulacra extending the entire distance from one to the other of these open- 

 ings, while they also possess an apical disc, composed of a series of ocular and 

 ovarian pieces (the latter pierced by genital pores), surrounding the anal open- 

 ing. Again, like the Cidaridse and some other Echinoids, and unlike any 

 known Crinoids, they were provided with powerful jaws; while they farther 

 agree with the Echinoids, and differ from all the known Crinoids, in the posses- 

 sion of articulating spines. 



We are aware the opinion has been expressed that Mclonitcs multipora was 

 attached by pedicel or jointed column, like the Crinoids — an error probably 

 originating from the occasional occurrence of specimens crushed together in 



* Traite de Paleont., iv, p. 257, 1857. 



f Synopsis Ech. Foss., p. xxvii, 1858. 



J Nat. Hist, des Zooph., Suites du Buffon, p. 461, 1865. 



I Brit. Palaeozoic Foss., p. 124, 1851. 



|] Wiegmann's Arch., i, p. 312, 1855. 



