12 SVEN LOVEN. OX A KECENT FORM OF THE ECHINOCONID^. 



Chalk as well as Jurassic, of Discoidea and Holectypus i), re- 

 present tlie epistromal protuberances as forming transverse, 

 straio-lit or waved strino^s of rounded or ovate beads or as 

 being more or less densely strewed. Nor are tliey absent 

 iu the Pygaster semisulcatus, Pl. 2, fig. 11, 14. They are 

 spread among tbe primary and smaller tubercles, and gathered 

 iu groups on the flanks of the interradia. Under the miero- 

 scope they present the appearance of sub-pedunciilated, glo- 

 bular, berry-like protuberances, such as are met with in the 

 young States of Arbacia and Salenia. But in the Pygaster 

 thev do not present the luxuriance so conspicuous in the re- 

 cent form, and do not produce the appearance of a double 

 lip described above. 



Specimens of Pygaster are rarely found with the calycinal 

 -system in its place and entire; in most cases it is löst, and 

 along with it the uppermost parts are gone of ambulacra and 

 interradia. The posterior portion of the periproct, hoAvever, 

 often remains unbroken. This is what has happened with the 

 recent specimeu. The calycinal system and portions of the 

 ambulacra and interradia are missing, and of the intcrradium 

 5 also mvich is löst, but of the periproct a considerable part 

 has been left entire. All this seems to indicate a disposition 

 of these parts nearly resembling that of the correspouding 

 parts in the orenus Pvsraster. 



The remark is near at hand that the specimen here de- 

 scribed may represeut only the young state of its species, and 

 in the absence of the calycinal system the question thus raised 

 cannot be answered satisfactorilv. In the parts remaining, 

 however, there is nothing of a dccidedly juvenile character. 

 The test is rather thick and has sufiered less from witherino- 

 thau dead tests of young specimens generally do; the tuber- 

 cles, the epistromal protuberances, and the depressed ambula- 

 crals have more of the adult than of the young. Perhaps also 

 it mav he said, that if its size as full-o-rown were more con- 

 siderable, it would not have escaped being caught by the 

 dredge. Littleness thereforc seems to be auother character by 

 which it departs from the extinct forms it revives, no less 

 than from the recent forms among which it lives. It is a 

 stranger to the present Echinoidean world, predominantly con- 



') Pal. FranQ. VI.. Crét. p. 4!>8. 516, Pl. 996. 997; VII, Pl. 1008— 

 101.3, 1016, 1017, 1019 etc. Ib. IX, Jura, p. 418, Pl. 104, 105, 107. 



