224 MR. S. O. RIDLEY ON THE CORALLIID^E. [Feb. 7, 



opera-glasses, or of two short globose bottles united by their sides ; 

 consists of two globose masses, often somewhat flattened at distal 

 end, 'separated by a more or less deep constriction, their surface 

 microtuberculate ; to the proximal extremity of each is attached a 

 short handle-like process, of variable shape, bearing several long 

 tubercles, and about one third the length of the larger lobes ; average 

 maximum size '053 mm. long by -053 mm. across the two lobes; 

 thickness of lobes, antero-posteriorly, about "044 mm. 



The thickness of the cortex appears to be correlated with the 

 smoothness of the hard axis in the stem (higher up this is distinctly 

 striated) ; for in the other species of Hemicoralliutn, H. secundum, the 

 thinner cortex appears to be associated with a striated stem. The 

 explanation (physiological) appears to be that the coenosarcal canals, 

 which would have grooved the surface of the axis, find sufficient 

 protection in the cortex when this is thick. 



Turning to C. {Pleurocorallium, Gray) secundum, Dana (U.S. 

 Expl. Exp., Zoophytes, vol. vii. p. 641, Atlas, Zooph. pi. Ix. fig. 1), 

 we find again the mode of branching to be substantially that in one 

 plane ; here too the polypes are said to be confined to the front or 

 sides of the branches, but to be borne mostly on small branchlets or 

 pinnae scattered over the edges and front of the main branches — an 

 arrangement differing from that of both the preceding forms, but 

 agreeing with that to be described below in the new species C. stylas- 

 teroides, with which this species further agrees in the growth in one 

 plane. Unfortunately the spicular characters are unknown ; but, 

 from resemblances which have been found to exist between this and 

 a form described below as a variety of it and agreeing in all generi- 

 cally important characters with HemicoralHum johnsoni, I have little 

 doubt of its similar generic identity with that species : therefore one 

 of the genera Pleurocorallium and HemicoralHum must give way, 

 and the former must stand, having precedence in description. 



HemicoralHum therefore = Pleurocorallium ; and HemicoralHum 

 johnsoni = Pleurocorallium johnsoni. 



Looking at the relations of C. nobile to the species described 

 below as new under the name of G. stylasteroides, we find a thin 

 cortex in both, a low polype-verruca, and a spicule differing only in 

 size ; and it is only in those characters which, as I have stated, I 

 beUeve to be less essential in the classification of this Order, viz. 

 mode of branching, colour, and form of axis {i. e. cylindrical or 

 oblong in section), that we find great differences ; and the first two 

 of these have been already seen to vary widely in C. rubrum, and in 

 their variation to approximate that species to C stylasteroides. 



No other recent species has been described. 



The only other species with which I am acquainted are the fossil 

 forms C. pallidum, Michelin (Iconogr. Zoophytol. p. 16, pi. xv. fig. 9), 

 from the Miocene of Italy and Tertiaries of Scinde, and C. beckii, 

 M.-Edw. and Haime (Distr. meth. polyp, palseoz. p. 188), from 

 the White Chalk of Faxoe. The former is distinguished from our 

 species by having the method of branching of C. nobile, viz. cylin- 

 drical branches given off at considerable intervals ; and it appears to 



