POURTALESI.E. 131 



of the Pourtalesiae in the isolation of the second row of plates of all the 

 interambulacra from the actinal primordial interambulacral plates by the 

 intrusion of the second row of ambulacral plates of all the zones. They 

 connect laterally in Arachnoides, Echinarachnius, Clypeaster, and Encope, 

 while the ambulacral and interambulacral zones are perfectly symmetrical 

 in Echinocyanus, Laganum, and Mellita; the latter genera holding to the 

 former much the same relation which the recent Ananchytids hold to the 

 modern Spatangoids. 



The discovery of so many recent Ananehytiddike Spatangoids would 

 seem to warrant the establishment of subfamilies including on the one 

 side, as Urechinida3 : Urechinus, Cystechinus, Pilematechinus, and Calymne ; 

 and on the other as Paleopneustidae : Paleopneustes, Linopneustes, Hotno- 

 lampas, Phrissocystis, Argopatagus, Genicopatagus, Palrcotropus, and Palaeo- 

 brissus. This would exclude from the Pourtalesia? a few genera at one 

 time associated with them, and limit the Pourtalesia? to Pourtalesia, Echino- 

 crepis, Spatagocystis, Plexechinus, and Sternopatagus. But the Pourta- 

 lesiae can hardly be considered, from what has been said here, as a group 

 equivalent to the Clypeastroids and Cassidulids, as has been suggested 

 by Loven. 



Among the Spatangoids a new genus of Pourtalesia? has been described 

 from the collection of the "Siboga" Expedition under the name of Sterno- 

 patagus, 1 differing in shape from that of any other Pourtalesia. It has 

 the marginal fasciole of Calymne, the abactinal system of Cystechinus 

 (C. Loveni) though there are four genitals in Sternopatagus and only three 

 in C. Loveni. The labium is separated from the sternum much as it is in 

 Plexechinus, which, however, has the compact abactinal system of Pourta- 

 lesia proper. If the figures of M. De Meijere are correct, its sternum has 

 nothing in common with that of Urechinus, as he states, the labium of the 

 former being separatedfrom the sternum, which is not the case in Urechinus. 

 The abactinal system of Sternopatagus is entirely different from that of the 

 Pourtalesia? ; the bivium is not separated from the trivium by the posterior 

 lateral interambulacra, its apical system as well as that of Sternopneustes 

 is quite that of Holaster and of the Ananchyticla?, and it also has its anus 

 on the lower side as Echinocrepis. 



The plates of the apical system of Echinocrepis are not as they have been 

 described by M. de Meijere; those of the bivium are well separated by the 



1 Sternopatagus Sibogse De Meijere. Die Echinoidea der Siboga-Expedition, p. 154. 



