I'.CIIIN'UIUKA. II. 



85 



111 llif last iianiL-d pajjcr 1)\ LaiiihtTl he evidently docs not lay so inticii stress on these two 

 different t>pes of plastron since he places the topical nieridosternous Menuthiasfcr in his faiiiih- 

 Acropidu" which otherwise comprises forms with the i)lastron plus on moins developpe, et dans !e 

 premier cas tonjonrs amphisterne ; he considers the genns Mcnulhiastcr as «une forme profondement 

 modifiee, avec tendance an retonr vers nil <;roni)cinent homogene des assules interambnlacraires et 

 dout la disposition exceptionellement meridosterne n'a qn'nne importance relative, incapable de pre- 

 valoir centre I'ensemble des antres caracteres, notamment le groupement des plaques apicales^ (p. 323). 

 This leads us to consider more closeh- the systematic value of the characters afforded by the apical 

 system in the Mfridostcnii. I ma\- then recall the differences occurring among the PourtalcsiidcB with 

 regard to the apical system: disconnected in the /'our/a/rs/'d-spccies; compact in Echinocrepis cuiicala, 

 disconnected in Ecli. sctigcra ; compact in S/fri/apafagus, disconnected in Spatagocystis. K\en if it is 

 scarceh' correct to admit species with compact and with disconnected apical systems into the same 

 genus (for which reason I have made Ecliinocr. sciigcra the t>pe of a new genus, see above p. 84), 

 uobod\- will doubt that all these genera are \-ery nearly related, and are riglitl)' referred to the same 

 family '. — Even among specimens of the same species there may occur rather great differences in 

 the structure of the apical system — see e. g. the two figures of apical s\-stems of Urccliiniis iiarc- 

 siaitns given by Agassiz (Pan. Deep-Sea Ech. p. 156. Figs. 226 — 27). There can thus be no doiil)t that 

 the apical system is of comparativeh- little systematic importance among the A/rridoslrnii, and it 

 seems to me very irrational to place the nieridosternous Minuthiaster among the amphisternous 

 <iAcropid(r on account mainl\- of its apical system, the more so as it differs, indeed, only very little 

 from the normal structure thereof in the A)iaiicliytida\ I^ikewise the fascicles are of comparatively 

 small SNstematic importance among the Mtridostcriii - I may recall e. g. the subanal fascicle of 

 Sicreopfi.custcs. the marginal fascicle of CalyiiDir, and the fact that in Urrcli. >iaresiamis some speci- 

 mens have a subanal fascicle, while other specimens show no trace thereof. 



It seems then beyond doubt that the nieridosternous and the amphisternous structure of the 

 plastron is the priiiiar\- systematic character among the higher Spatangcids. On grouping the genera 

 accordingly, we get in the group of the J/^/'/V/rAf^v//'/: the Ananckyfhidcr (or Echinocoryf/iidce), Urcchinidcc 

 and Pourfalcsiida-. in the group of the Aniphisfenii: the rest of the Spntaiigidce. (I cannot here enter 

 on a discussion of the families of the Aiiip/iisfcri/i). It is at once seen that these two main groups 

 are very natural, another sign of the correctness of using the structure of the sternum as the i)rincipal 

 character. 



Without giving detailed diagnoses of the families of Mcridostcriii I ma\- point out what lo me 

 appear their main characters. In the Vrcchiiiidu- the second plate of all the interainbulacra is a single 

 plate — probabh- not the result of the fu.sion of the plates a. 2 and b. 2, as thought b\- Lovcn, 

 but of a nieridosternous arrangement of these plates in all the interambulacra, as thought b\- Lam- 

 bert-. The Urccliiiiidtr thus represent a separate branch from the Aiiaiuhylidd-, characterized b\- the 



■ .Agassiz, it is true, doubts that Sieynopalagus is really a Pourtale.siid, but — in my opinion without sufficient 

 reason. CTregory (in Ray Lankester's Treatise on Zoology. III. p. 321) places Echinocrepis and Spa/agocys/is in the family 

 Spalangidcv, even in two different sections, whereas Pourtalcsia is kept as a distinct family. This classification is, indeed, so 

 absurd, that it needs no refutation. 



2 In the great Monograph of Echinocorys (Mem. Mus. d'hist. nat. de Belgique. II. 1903) p. 26 Lambert says: en 

 reaUte, je ue crois pas que le systeme perisouiatique interradial des Echinides comporte une seule plaque double, pas niemc 



