^journ^i. FebTmS:''] RoycU Microscopicol Society. 87 



The predominant type of the spicula in this genus appears to 

 originate from an irregular tuberculate fusiform condition, which 

 evinces a tendency to become eminently proliferous (Plate XLI., 

 Figs. 40,41). Associated with these, attenuato-bistellate and echinato- 

 clavate spicula are of frequent occurrence, these latter occupying 

 the superficial layer of the coenenchyma. 



Plexaura racemosa, Yal. et M. Edw., possesses spicula corre- 

 sponding exactly to what obtains in Gorgonia proper, and to which 

 genus it should in all probability be referred ; additional evidence in 

 support of the proposed re-arrangement of this species is fui'nished 

 by Milne Edwards' remark that it seems to establish the jjassage 

 between the genera Eunicea and Gorgo7iia. 



Gorgonia alba, Lamk., referred with doubt to Eunicea by Milne 

 Edwards, contains spicula agreeing essentially with the type 

 j^redominant in Leftogorgia to be afterwards described, and to 

 which genus it is probably referable. The spicula of Plexaura 

 eburnea, Val., not alluded to by Milne Edwards, also agree with the 

 same type. 



Gorgonia noduUfera, Lamk. (Plexaura (?) M. Edw.), abounds 

 with spicula agreeing with a form predominant in Verrucella gem- 

 macea, and which wiU be again referred to when describing those of 

 that species. Kolliker retains this species in the genus Plexaura, 

 but probably had not an opportunity of consulting the type spe- 

 cimens ; he likewise adds to it Plexaura Ehrenhergii, KL, P. an- 

 tipaihes, Kl. {Gorgonia, Esp.), and P. duhia, Kl. (G. aniipathes, 

 var. Esp.). 



Plexaurella, Klk., Plexaura dichotoma and vermiculata, 

 M. Edw., with other allied species, have been formed into the new 

 genus Plexaurella by Kolliker, on account of the difference they 

 jjresent in the structure of their axis and in the contour of their 

 spicula from all the ordinary Plexaurse. The axis in this genus 

 contains a large amount of carbonate of lime, and the spicula are 

 very characteristic. These last assume a bi- tri- or quadri-partite 

 outline, the latter form often bearing a strong resemblance to some 

 elegant tropical PapiHo. They are for the most part more or less 

 bilaterally symmetrical, having a smooth zone in the centre, with 

 richly tuberculated alae on either side. Characteristic forms from 

 Plexaurella dichotoma are represented at Plate XLI., Figs. 47-51. 



To the species already referred to, KoUiker annexes Plexaurella 

 'crassa [Gorgonia, Esp.), Plexaiirella ancejjs and nutans (Eunicea 

 of Duch. et Mich.), and Gargoiiia f areata, Lamk. To these 

 should evidently be added Gorgonia heteropora, Lamk. (Plexaura 

 of Lamx.), the spicula in this species agreeing precisely with the 

 form predominant in P. dichotonna. 



Gorgonia. — Polypary arborescent, more or less flabeUate, branch- 

 ing irregular dichotomously ; ramuscules free, almost cyhndrical. 



