Prof. F. J. Bell on the Laganidse. 131 



" exhibemus in/' and that all the accusatives that follow are 

 in the plural number. In his article " Scutelle " (1827), de 

 Blainville exhibits no acquaintance with the work of Gray j 

 but in 1830, in the article " Zoophytes," he adopts and uses 

 Gray's term Lagana*. Finally, L. Agassiz returned, in 

 1841, to the correct and ancient form of the name. 



2. Structural Characters. — -There would appear to be some 

 considerable difficulty, not so much in judging as to the forms 

 which belong to the Laganidse, as in the determination of the 

 value of the characters of the species. We may justly assume 

 that^ no greater weight, at any rate, than that which is due to 

 specific characters can be given to the general form of these 

 always flattened subpentagonal Echinids ; nor do they, with 

 their simple spines and their fairly regular tubercles, offer us 

 therein any useful mark of distinction. As shall now, how- 

 ever, be shown, there are two points of value on which some 

 importance has been laid — the genital pores and the internal 

 structure of the test. The pores may be four or five in number, 

 intra- or extrapetaloid in position j and the septa or walls, 

 which unite the actinal and abactinal plates, vary in the ex- 

 tent of their development. 



In his classical monograph on the Sculellidae, Professor 

 Louis Agassiz directs attention to the characters of the genital 

 pores in the following words (p. 107) : — u il est un point de 

 Porganisation des Laganes qui offre de graves difficulty, c'est 

 la variete qui rhgne dans le nombre des pores genitaux, une 

 partie des esp&ces en ay ant invariablement cinq, tandis que 

 d'autres n'en ont que quatre. J'ai vainement cherche k 

 rattacher ce fait k quelque autre caract&re constant de l'orga- 

 nisation ; mais n'ayant reconnu dans la structure de l'appa- 

 reil genital a Finterieur aucune difference entre les espkces qui 

 ont quatre pores et celles qui en ont cinq, j'ai du renoncer 

 provisoirement k les diviser." And a similar remark is made 

 by Desor f : u Comme sous tous les autres rapports la ressem- 



blance est tr&s 



les deux types. 



A somewhat different aspect is given to the matter by the 



remarks of Mr. Alexander Agassiz on p. 520 of his well- 

 known c Revision.' u Agassiz had already hinted at the 

 probable generic separation of L. Peronii from Laganum; 



* The possessor of the ' Revision of the Echini ' may make, therefore, 

 the following corrections on p. 137 in the " Synonymy " of the generic 

 name : — After Scutella in thick letters should follow Lagana, Gray, 1825, 

 Ann. Phil. n. s. vol. x. p. 427 ; and the date 1827 after the name of de 

 Blainville should be altered to 1830. 



t Synopsis des Echinides fossiles, p. 228. 



cru 



n 



