g. ECHINOIDEA. II. 



essentially from those of other Pourtalesice ". — These differences in the pedicellarice are certainly not 

 very important, and probably Ecli. ciiiirafa will also prove to have both ophicephalous and rostrate 

 pedicellariie. The more important are the differences in the apical s\steni and the bi\ial ambnlacra, 

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

 it necessary to create a new genus for sctigera. for which I nia\- propose the name Cystocrepis u. g. 

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

 a generic character. 



Regarding tlie svstematic position of the family PouK/dlrsi/da" 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 

 nic that he has shown be\ond doubt that the Pourtaksiidcc represent a very special development 

 from the Anniicliytidcr, the highly interesting genus .y/(-/-,'/iy/«%'-«.s- being in niau\- respects a transitional 

 form between the Poin/alcsiida- and the ^li/aiichytidir , though alread\ decidedly belonging to the 

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

 chylidce whereas, on the other hand, he refers the genus Flcxcchiiius — in mv opinion undoubtedly 

 an Urechinid — to the PuJirtalcsiidcc]. 



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

 le plastron des Spatangidess)^ that the difference between the meridosternous and the amphisternous 

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

 the recent Spatangoids may be divided into Mcridostcrui and Aiiip/iisfcnii. names given by Loven, 

 wlio (lid 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 interambulacrum, something like what is found in 

 Dysastcr and the Cassidiilidu-. To be sure, Agassiz (Pan. Deep-Sea Ech. j). 164) thinks that Ivambert 

 <has hini-sclf given us the best jjossible 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 >oung (PI. 99. 1—5, 8) seems to settle this question in favour of Loven's view». 

 But, as is easily seen, the young Ahatiis 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 labrum, 

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

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

 as yet no sternum developed, the plates 5. a. 2 and b. 2 ])eing rather small, Ihougli distinctly larger 

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

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

 yoimg Palcropncuslcs crisiatus in the <;Blake»-Echini (1^1. XXI. 11) as showing comment on doit com- 

 prendre le developpement amphisterne du plastron, c^ui proccde d'un etat originaire oil les plaques 

 sent semblables dans toutes les aires interradiales, connne chez les Cassidulides . 



' Whether it is the ophicephalous pedicellariie, which are liriUiaiit ,i;lass.v heads staiuling out hke niinialure .spheres 

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

 2 Bull. Soc. de rYoiine. 1892. 

 J Note sur quelques Ivchinides cretaces du Madagascar. Bull. Soc. Geol. dc I'rance, 3. .Ser. 24. 1S96. p. 323. 



