4 ME. P. H. CAEPENTER ON THE GENUS ACTINOMETRA. 



Dc Preniinville's specimen was found on the keel of a vessel which had come from a 

 warm climate ; it had ten arms and twenty cirrhi, and was named by him Antedon gor- 

 gonia. He gave no further description of it, but simply referred to the figure of Stella 

 decacnemus rosacea, Linck, in the ' Encyclopedie Methodique ' \ which represents the 

 ordinary European Comatula rosacea, as it is now called. 



This species, however, is not identical with De Premiuville's Antedon gorgonia, which 

 was referred by Lamarck 2 to his Comatula carmata, under which name he described 

 some specimens brought by Peron from the Isle de Prance. Nevertheless the two 

 species resemble one another in some important points, viz. the presence of ten arms, 

 of a central or subcentral mouth, and of an excentric anal tube. 



In 1815 Leach 3 rescued the three genera contained in Linck's classis CrinitcB 

 from the confusion of the Liunean genus Astcrias, and united them into one genus, 

 Alecto, comprising three species, viz. Alccto europcea (= Decacnemus rosacea, Linck), 

 Alecto horrida (= Caput-Medusoe, Linck, or Asterias multiradiata, Linn.), and Alecto 

 carinata (which seems to have been the same as De Premiuville's Antedon gorgonia). 



Leach defined Alecto as having the " os inferius, irregulare," a description which would 

 suit equally well either for the true mouth or for the anal opening, though perhaps 

 more applicable to the former. He seems, however, like his predecessor De Preminville, 

 to have regarded the mouth as situated at the extremity of the anal tube ; for in the 

 explanation to Schweigger's figure 1 of Leach's specimen of Alecto horrida the latter is 

 described as the " rohrenformig hervorstehender Mund." It is obvious, therefore, that 

 we cannot make any use for systematic purposes of the definitions of Antedon and Alecto 

 as given by Leach and De Preminville respectively, as far as the position of the mouth 

 is concerned. 



Schweigger's figure of the disk of Alecto horrida shows clearly enough that the five 

 trunks of the ambulacral grooves converge towards the centre of the disk, as in Antedon 

 rosacea (Alecto europcea, Leach), Plate I. fig. 1. Leach's Alecto horrida was therefore 

 a true Antedon in the modern sense of the term, although belonging to that division of 

 the o-enus in which the repetition of the bifurcation of the ten primary arms is carried 

 to a great extent. 



(§4) Leach was apparently unacquainted with the memoir of Preminville; but the 

 same was evidently not the case with Lamarck (1S1G), who, like Leach in the previous 

 year, united Linck's three genera into one, to which he gave the very appropriate name 

 Comatula 5 . His definition of the genus differs but little from that given for Antedon 

 five years previously by De Preminville, whose original specimen Lamarck seems to have 

 examined ; and it is difficult to see why he did not adopt the name Antedon to designate 

 the genus, which, like Leach and De Preminville, he clearly distinguished as belonging 

 to a different type from the Asteridse, Ophiuridoe, and Eur y ale. 



1 Partie des Vers, pi. 42. fig. G. 3 Tom at. p. 534. 



3 Zoological Miscellauies, vol. ii. p. 61 : London, 1815. 



4 Beobacht. auf naturhistorischen Reiseu, p. GO, and Taf. iv. fig. 42 : Berlin, 1819. 



5 Turn. cit. p. 530. 



