1889.] RARE SPECIES OF PLEXAURIDS. 49 



The present species is erect, branching, elegant, not at all closely 

 bushy ; there is no spreading base, but the trunk is rather wide, 

 being about 3 cm. in diameter ; the branches are flattened at the 

 points of bifurcation ; the secondary trunks give rise to brandies, 

 which do not ordinarily branch more than five times, so that many 

 of the terminal twigs are as much as 35 cm. long ; these terminal 

 twigs are about 5 mm. in diameter. There are a few nodosities. 

 The cortex is fairly thick, the calyces numerous, irregularly scattered, 

 rather large pits, so that the general appearance is not unlike that 

 of P. porosa. Axis brownish, impregnated with calcareous salts, 

 and the species belongs, therefore, to the genus Plexaurella and not 

 to Plea-aura. The characteristic spiculation is shown in the accom- 

 panying figure. 



Had. West Indies. 



5. Plexaurella vermiculata. (Plate Ilf. fig. 5.) 



Gorgonia vermiculata, Lamk. 



Plexaura vermiculata^ i\\. ; see Milne-Edwards & Haime, Corall. i. 

 p. 156. 



Plexaurella vermiculata, Kolliker, Icon. Histiol. p. 138. 



There is not, I think, sufiicient reason for distinguishing as the 

 type of a distinct species a specimen labelled by Dr. Gray as Plexaura 

 porosa, but which is certainly a Plexaurella, inasmuch as it has 

 deposit of calcic carbonate in its axis. It presents some slight points 

 of difference from P. vermiculata, as described by Milne-Edwards 

 and Haime, and there is not an absolute identity of spiculation. 

 There cannot, I think, be any doubt that there has been a tendency 

 to neglect the variations possible in these forms, and it is better to 

 refrain from " splitting " species. 



In the specimen under consideration the calices are nearly as 

 closely packed as in P. porosa ; the terminal branches are often 

 rather less than 8 mm. in diameter, and the main trunks are from 

 12 to 16 mm. across, whereas Milne-Edwards gives 8 mm. for the 

 former and 9 to 10 mm. for ihe latter ; no statement, however, is 

 made as to the height of the whole mass ; in the case of the British 

 Museum specimen it is rather more than 60 cm. and all the tops are 

 a little broken off. 



The cortex, which is thick, is of a lightish brown colour ; the axis 

 is of a light brown colour. The axis is flattened at the angles of 

 division, and there appears to be no tendency to the formation of 

 nodes ; some of the terminal branches are more than 1 5 cm. long. 



The spicules are, as the figures show, short, but somewhat irregular 

 in form. 



EXPLAJf ATIO]S^ OF PLATE in. 

 Spicules of Plexaura and Plexaurella, X 180. 

 Fig. 1. Plexaura priiicipalw, p. 47. 



2. Plexaura suffruticosa, p. 48. 



3. Plexaurella affi?iis, p. 48. 



4. Plexaurella anguiculoides, p. 48. 



5. Plexaurella vermiculata, p. 49. 



Proc. Zool. Soc— 1889, No. IV. 4 



