8 4 



ECHINOIDEA. II. 



essentially from those of other Pourtalesise '. — These differences in the pedicellarke are certainly not 

 very important, and probably Ech. cuneata will also prove to have both ophicephalous and rostrate 

 pedicellarhe. The more important are the differences in the apical system and the bivial ambulacra, 

 so important, indeed, that it seems quite unnatural to unite the two species in one genns. I think 

 it necessary to create a new genns for sefigera, for which I may propose the name Cystocrepis n. g. 

 Also the difference in the shape of the test is very conspicuous, though perhaps not reliable for 

 a generic character. 



Regarding the systematic position of the family Pourtalesiida I quite agree with de Meijere, 

 who has in a most skilful manner discussed the whole question ( Siboga -Ech. p. 160 — 71); it seems to 

 me that he has shown beyond doubt that the Pourtalcsiidcr represent a very special development 

 from the Ananchy tides, the highly interesting genus Sternopatagus being in many respects a transitional 

 form between the Pourtalesiidtz and the Ananchytidm , though already decidedly belonging to the 

 former family. (I can not agree with Agassiz, who thinks Sternopatagus more related to the Anan- 

 chytidm whereas, on the other hand, he refers the genus Plexechinus - - in my opinion undoubtedly 

 an Urechinid — to the Pourtalesiida). 



It is Lambert's merit to have first emphasized (in his excellent Etudes morphologiques sur 

 le plastron des Spatangides») 2 that the difference between the meridosternous and the amphisternous 

 structure of the plastron in the Spataugoids is of primary systematic importance, so that the whole of 

 the recent Spataugoids may be divided into Meridosterni and Amphisterni, names given by Loveu, 

 who did not, however, clearly point out the importance of these different structures, which he had 

 detected. The two types cannot be derived one from the other, but must have derived from forms 

 with a simple, unmodified structure of the odd iuterambulacrum, something like what is found in 

 Dysastcr and the Cassidulidm. To be sure, x\gassiz (Pan. Deep-Sea Ech. p. 164) thinks that Lambert 

 «has himself given us the best possible proof of the accuracy of Loven's view of the development of 

 the amphisternal from the meridosternal plastron. The development of the adult amphisternal Abatus 

 from a meridosternal young (PI. 99. 1—5, 8) seems to settle this question in favour of Loven's view». 

 But, as is easily seen, the young Abatus represented in PI. 99. 3 does not show the slightest trace of 

 a meridosternous structure, both the plates 5. a. 2 and b. 2 being in wide contact with the labruin, 

 whereas the meridosternous structure, as is well known, means that only one plate (b. 2) is in contact 

 with the outer end of the labrum. The specimen figured by Agassiz might perhaps be said to have 

 as yet no sternum developed, the plates 5. a. 2 and b. 2 being rather small, though distinctly larger 

 than the following ones. At most this stage can show that the amphisternum is derived from a primitive 

 structure, where no sternum is developed as yet; in this way Lamberts refers to the figure of a 

 young PalcEOpneustes cristatus in the Blake -Echini (PI. XXI. 11) as showing comment on doit com- 

 prendre le developpement amphisterne du plastron, qui precede d'un etat originaire ou les plaques 

 sont semblables dans toutes les aires interradiales, comme chez les Cassidulides . 



1 Whether it is the ophicephalous pedicellarise, which are brilliant glassy heads standing out like miniature spheres 

 on the dark test» (Pan. Deep-Sea Ech. p. 147) I dare not say. 



2 Bull. Soc. de l'Yonne. 1S92. 



3 Note sur quelques Echinides cretaces du Madagascar. Bull. Soc. Geol. de France, 3. Ser. 24. 1S96. p. 323. 



