416 PROF. F. J. BELL ON THE ECHINOMETRID^. [Mar. 15, 



It may, at the present juncture, be convenient to recapitulate and 

 extend the results of recent investigations into the characters of the 

 regular Echinoidea. 



A classification of the regular Echinoidea is not, as it seems to 

 me, quite so impossible a matter now as it was a few years ago ; the 

 discovery, by Mr. Charles Stewart \ of the internal gills of Cidaris, 

 and the extension and independent confirmation of that result by 

 Dr. Hubert Ludwig^, justifies us in accepting the division into 

 Branchiata and Abranchiata, proposed by the latter naturalist ^ 

 Although Johannes Midler had distinctly denied the presence of 

 external gills in Cidaris*, Prof. Alex. Agassiz discovered gill-cuts 

 in the figures of that illustrious anatomist, but only, I fear, by 

 reflecting on the character of the artist, who represents five slits 

 in the median line of the interradial areas ; to this, however. Dr. 

 Ludwig has already directed attention. 



Readers of the just-mentioned naturalist's essay will remember 

 that he proposes to separate the Echiuothuridae from the rest of 

 the branchiate regular Echinoidea on the ground of the difference 

 in the characters of the buccal plates. 



Unfortunately the British-Museum collection contains no specimen 

 of Asthenosoma, although an American collection is in possession of 

 a specimen "which the Museum owes to the kindness of Prof. 

 Thomson, collected by the Porcupine Expedition ;" and I am 

 therefore unable to give any independent judgment as to the point 

 at issue between Sir \V. Thomson and the writer of the just-quoted 

 sentence on the one baud, and Dr. Ludwig on the other. To say 

 nothing of the fact that the Porcupine Expedition was fitted out at 

 the national expense, the present state of the question affords ample 

 evidence of the advantage of rare and typical specimens being 

 deposited in a central and national institution. 



Conflicting as the statements are, those of Dr. Ludwig are so 

 explicit, and are made with so distinct a knowledge of the opinions 

 of his predecessors ^ that I think it is, for the present at any rate, 

 the view to which one ought to incline. The Echiuothuridae, then, 

 though Brancliicda, are distinguished from the rest by having more 

 than one pair of each series of ambulacral plates carried on to the 

 buccal membrane ; they may consequently be distinguished as a 

 2^ohjlepi(l as compared with a decaleind series. 



This decalepid series includes the Diadematidoe, the Arbaciadse, 

 the Echinidae, and the Echinometridse, together with the Salenidse. 

 These last are at once to be separated off from the rest by the 

 characters of their apical area; they are palceoproctous forms, as 



1 Trans. Linn. Soc. (2). i. p. 569. 



^ Zeitschvil't fiir ms8. Zool. xxxiv. pp. 70-87. 



3 Prof. Alex. Agassiz gives no information, in his preliminary diagnosis, as 

 to the gills of Aspidodkule)?ia. 



4 Abh. Berl. Akad. 1853, p. 146. 



* He speaks of " ein ganz fundanientaler und bis jetzt nicLt beacbteter 

 Gegensatz zu den Cidariden." The possession of buccal plates being a charac- 

 teristic of tlie Desmostieha, the differences which obtain with regard to them 

 are to be insisted on in the arrangement of the constituent families. 



