32 PANAMIC DEEP SEA ECHINI. 



Cextrocidaris A. Ag. 



In his important paper on the Cidarida? of Japan, 1 Doederlein very 

 properly objects to the position of Goniocidaris canaliculata in the genus 

 Goniocidaris, which he would place in a remote section of Dorocidaris, 

 if we limit it to species in which the bare ambulacral and interambulacral 

 spaces are found at the angles of the median lines of these plates. The 

 discovery of a species of Cidaris allied to G. canaliculata leads me to 

 suggest that it, as well as the species here described, be transposed to a 

 new subgenus, Centrocidaris, including it and G. canaliculata ; - the species 

 all being characterized by the broad bare space in the ambulacral and 

 interambulacral areas. This would seem to indicate the affinities of Gonio- 

 cidaris to be more remote from the Dorocidaris group and more closely 

 related to the type of Goniocidaris canaliculata, and finally with the limitation 

 <>f tlic bare pits to the angles of the plates we come upon the genus Gonio- 

 cidaris proper. 



Doederlein has in his interesting account attempted to subdivide the 

 recent ami fossil Cidaridse into a number of groups, many of which have 

 been based either upon the study of recent species or of fossils alone. 

 He has succeeded in making an excellent classification. Perhaps the most 

 interesting of his observations are those relating to the existence of furrows 

 on the outer edge of the ambulacra of some of the Jurassic Echini. This 

 feature recalls a similar structure in the plates of the Eocidaridai. It must 

 have rendered the test of these genera more or less flexible. This flexi- 

 bility was attained in a very different way from that of the Echinothurise ; 

 in the Cidaridae it was lateral, in the Echinothuria^ to great extent vertical. 



I can see no reason for referring G. canaliculata to Stereotidaris, as has 

 been suggested by Dr. Mortensen. 3 Referring a living species to genera 

 established for fossil species is so contrary to Mortensen's principles that I 

 cannot understand his reasons for referring to Porocidaris, Ste/rocidaris, and 

 Arbacina some living species, and rejecting other similar references merely 

 because they were based upon fossil species. But to Mortensen affinities as 

 usually recognized by most writers on Echini have no interest and have no 

 value when not based on the pedicellaria>. 



1 Japanische Seeigel, Inc. cit, p. 10. 



2 I had, in 1863, when describing G. canaliculata, originally placed it in the genus Temnechiuus, 

 a name preoccupied by Cotteau (Bull. M. C. Z., I. p. 18). 



3 " Ingolf " Echinoidea, p. 29. 



