436 MR. F. J. BELL ON ECHINOC1DARIS. [May 6, 



5. Note on the Number of Anal Plates in Echinocidaris. By 

 F. Jeffrey Bell, B.A., Magdalen College, Oxford, 

 Zoological Department, British Museum, F.Z.S. 



[Eeceived April 23, 1879.] 



If any one anatomical fact was thought to be certain with regard 

 to the Echini, it was the presence, as a constant mark of differentia- 

 tion, of four plates and four plates only in the anal region of the 

 species of the genus Echinocidaris. Thus not only does the diagnosis 

 of Desmoulins (183o) include the words " pieces terminales auales 

 au nombre de quatre seulement," and that of Gray (1835, Arbacia) 

 "anus valvis quatuor spiniferis tectus," but the definition given by 

 Prof. Alex. Agassiz 1 of the family Arbaciadae states among other 

 characters that <c the anal system consists of only four large triangu- 

 lar plates." Prof. Troschel, in an elaborate article on the genus 2 , 

 exhibits not the slightest doubt as to the validity of this character, 

 and expresses himself in the following words : — " Das Periproct ist 

 durch vier dreieckige Platten geschlossen " 3 . In a later publica- 

 tion than his ' Revision ' (in the Zoological Results of the Hassler Ex- 

 pedition 4 ), Prof. Alex. Agassiz sounds the first inharmonious note. 

 Troschel (so certain was he of the great value of these four anal 

 plates) had, on account of the presence of five anal plates in some 

 Parasalenice, separated them from the Echinocidaridse, in which family, 

 as he imagined, Agassiz had placed them. Roused, apparently, by 

 his criticism, the American naturalist took the opportunity afforded 

 him by the arrival of additional specimens of E. dufresnii to point 

 out " that it is quite remarkable that in the few specimens existing 

 in the British Museum and in our collection, there should be two 

 specimens having five anal plates instead of the normal number of 

 four in the other species of the genus " 5 . As there are two speci- 

 mens in the British-Museum collection in which there are five anal 

 plates, and as, on the other hand, the collection made by Dr. Cun- 

 ningham, " of quite a number of specimens," passed, as Prof. Agassiz 

 informs us, through his hands before the ' Revision ' was published, 

 and that without the peculiarity in question being there noticed, it 

 would be possible to read the (not too perspicuous) sentence which 

 I have just quoted in any one of the three following ways : — 



(J ) Both the specimens referred to are in the British Museum ; 

 (2) neither specimen is in the British Museum ; or (3) there is, 

 to Prof. Agassiz's knowledge, one specimen in each of the collections 

 mentioned. I am inclined to think that this last construction is the 

 one which the words were meant to bear ; and I am supported in this 

 belief by the difference between the two specimens from Dr. Cun- 



1 Eevisiou of the Echini, p. 399 (1872-1874). 



2 Archiv fiir Naturgeschii'hte, xxxviii. p. 293, xxxix. p. 308. 



3 Op. cit. xxxviii. p. 298. 



4 Illustrated Catalogue, Mus. Comp. Zool. viii. p. G (1874). 

 3 Cat. M. C. Z. viii. i. p. 6. 





