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



period dawns upon us, the Spatangidce, universally Adete or Prymnadete, that is: devoid 

 of fascioles or provided with a peripetalous or lateral one only, but never with a 

 snbanal fasciole, were of a short and high, or globose form, as though not very far 

 removed from a pristine spheroidal type still unseen by us. Genera such as Hemiaster 

 Desor, powerfully developed and abundant in species, prevailed in the Cretacean seas; 

 in all of them the vertical dimension was considerable relatively to the transverse, 

 even so as to exceed it, andt he longitudinal dimension did not very largely surpass the 

 ti'ansverse. The dorsal and ventral halves of the test were generally conformable in 

 outline, the ventral being even more or less convex, the front ambulacrum Avas rarely 

 deep, the periproct sub-dorsal, and the stomo-proctic axis made with the longitudinal a 

 not very acute angle. The thickset form of these antique Spatangi strongly contrasts with 

 the elongated build of Pourtalesia Jeffreysi. Nor is it that the contrast beconaes less 

 striking, when in a few genera of the middle Cretaceous time the calycinal part of the 

 test is strongly raised, and at the same time di-awn forward so as to make the front 

 almost vertical, as is the case in certain species of Cardiaster and the closely allied 

 Infulaster Hagenow. Of this remarkable form I have been able, through the kindness of 

 Dr C. A. DoHRN of Stettin, to compare a cast ^). At the first glance there seems to be 

 some little resemblance to Pourtalesia, in the convexity of the ventral surface, in the 

 vertically raised forepart with its slightly sunk ambulacral groove and in the caudal 

 part projecting a little beyond the anal region, a feature shared in a higher degree 

 by some Cassidulid». But with these really unesseutial features the resemblance ceases, 

 and, as will be seen hereafter, Pourtalesia in characteristics of primary importance 

 departs very far from those Cretaceous types. Nor is this dissimilarity diminished in 

 any respect when in the course of geological time great changes are seen going on in 

 the structure and general conformation of the Spatangean type, and other forras are 

 introduced, Prymnadete as well as Prymnodesmic, thoroughly different from their 

 predecessors, in the calycinal system opening posteriorly ^) for the reception of the 

 restored central piece and costal 5, and in the test discarding the high and thickset 

 build, and assuming more and more the lengthened and depressed form with a flattened 

 ventral surface, prevalent among the Tertiary, and still more among the existing species. 

 But in the whole number of forms, in which this change has been brought about, 

 there is not one that comes near Pourtalesia in the cylindroid build of its skeleton, 

 and the shortness of its frontal part as defined by the paired ambulacra of the trivium, 

 compared to the lengthening of its hinder and by far greater portion. 



It is also in vain looking among the older Spatangidas for anything that may be 

 said to resemble that most striking feature, the bending in upon itself of the test, by 

 which the deep infra-frontal recess is produced, Avith the oesophageal opening at its 

 bottom. Among those forms that first come in sight, in the oldest Cretacean beds, 

 Anancites ^) has the five ambulacra all nearly uniform, the front ambulacrum dififering 



') The collections oiice made by Fr. v. Hagenow (b. 1797, d. 1865), who was blind during the last 

 cight years of his life, at present form part of tlie Pomeranian Museum at Stettin. Dr C. A. Dohbn 

 and his son Dr II. Dohrn were good enough to search it for tlie original specinien of Infulaster, but 

 withont SHCcess. Casts in plaster of Paris were however found, evidently taken from it. 



-) Études p. 12, 83. '^) Ib., pl. XXIV, fig. 181. 



