440 MR. p. H. CARPENTER ON THE GENUS ACTINOMETRA.. 



On the Grenus Actinometra, Miill., with a morphological account 

 of a new Species (^A. polymorphd) from the Philippine Islands. 

 By P. Herbert Carpenter, B.A., Biological Master at Eton 

 College. Communicated by Dr. William B. Carpenter, 

 P.E.S., F.L.S., &c. 



[Bead June 21, 1877.] 

 (Abstract *.) 



The ndsmeActinometra was given by Johannes Miillerf to those spe- 

 cies of the firenus Gomatula (Lamarck) in which the tentacular 

 furrows of the arms unite on the disk into less than five principal 

 trunks or ambulacra converging towards the peristom. Until the 

 time of Miiller, Leach's genus ^Zee^o was used as equivalent to the 

 Comatula of Lamarck ; but the application of this name was limited 

 by Miiller, who used it in contradistinction to Actinometra, to de- 

 scribe the more common species of Comatula, in which five prin- 

 cipal groove-trunks or ambulacra radiate outwards from the pe- 

 ristom, and subdivide symmetrically into more or fewer branches 

 proceeding to the diiferent groups of arms. 



The position of the mouth in Alecto might be either subeentral 

 (in no Comatula is it absolutely central), or more or less excentric, 

 sometimes even marginal ; but any Comatula in which five ambu- 

 lacra reached the peristom, whatever the position of the mouth, 

 was referred by Miiller to this genus, the sole distinction between 

 it and Actinometra being the presence of five or fewer principal 

 ambulacral trunks. 



From the time of Miiller until now, the genus Actinometra has 

 remained as he left it, though more than one author has remarked 

 upon the unsatisfactory nature of its distinctive characters. 

 Leach's name Alecto, however, has gradually passed into disuse, 

 having been partially replaced by De Freminville's name Antedon, 

 a precise definition of which has been given by Mr. Norman J. 



Antedon, like Alecto, was originally equivalent to Comatula ; but, 

 according to Mr. Norman's definition (which has been universally 

 adopted), it is now used to designate those forms only in which 



* [The memoir in full, with illustrations, will subsequently appear in the 

 Society's Transactions. — Ed.] 



t " Ueber die Gattung Comatula, Lam., und ihre Arten," Abhandlungen der 

 Berlin, Akademie, 1849. 



\ " On the Genera and Species of the British Echinodermata," Ann. & Mag. 

 Nat. Hist. ser. 3, vol. xv. p. 98, 



