ME. P. H. CARPENTER ON THE GENUS ACTINOMETRA. 15 



Aclinometra. The latter was erected into a separate genus by Dujardin, who limited the 

 application of the name Comatula to those forms only which had been described as 

 Alecto by Midler — those, namely, in which five main groove-trunks reach the mouth, 

 irrespective of its position, to which Midler seems to have attached no importance as a 

 character of any systematic value ; so that Dujardin, following him, says of the mouth 

 of Comatula (i. e. Alecto) that it is only " ordinairement au centre " \ 



Further, Dujardin, though really employing the name Actinometra in the same sense 

 as Midler did, does not describe it in the same way ; he takes no account of the number 

 of groove-trunks reaching the peristome, to which Midler attached so much importance, 

 but simply says 2 , " Ce genre ne differe guere des vraies Comatules que par la position de 

 l'anus au centre et de la bouche au bord du disque. II en resulte que les gouttieres 

 ambulacraires, au lieu de se rendre a la bouche en suivant la direction des bras comme 

 chez les Comatules, s'inflcchissent et suivent le contour du disque." Dujardin adds, 

 with perfect truth, that the distinctive characters of Actinometra are hardly yet suf- 

 ficiently established. It will be shown, further on, that his definition of the genus is 

 really the correct one, and that we must refer to it all those forms of Alecto (Comatula, 

 Dujardin) in which, as described by Midler 3 , the anal tube occupies the middle of the 

 disk, " so dass der Mund seitlich gegen den Rand der Scheibe riickt, ohne dass die 

 Ambulacra ihre symmetrische Vertheilung auf die 5 Armstamme einbiissen " (PL I. fig. 4). 

 As Midler had only employed the names Alecto and Actinometra to designate sub- 

 ordinate types of the Comatula of Lamarck, it is rather unfortunate that Dujardin 

 should have erected the latter into a separate genus, in contradistinction to Comatula, 

 and restricted this name to the Alecto of Midler ; for we now know, as mentioned in 

 section 5, that most of the species described as Comatula by Lamarck belong really to 

 Actinometra, not only in the somewhat limited sense in which this name was used by 

 Midler, but also in its wider application as employed in this memoir. 



Thus, for example, Midler stated expressly i that Lamarck's original specimen of 

 C. Solaris in the Paris Museum is identical with the large Vienna specimen, also bearing 

 the name of C. Solaris, Lam., which he made the type of his new genus Actinometra. 



Dujardin, however, paid no attention to this identification of Midler's, and described 

 the two specimens as C. Solaris and Act. hmperialis respectively, simply on the basis of 

 Mailer's original diagnosis, published before his visit to Paris. Dujardin thus made 

 not only two different species, but also two different genera, out of the same type, while 

 he makes a third species out of the Asterias pectiuafa of the Lund Museum, which 

 Midler regarded as a variety of Actinometra Solaris. 



I have examined a considerable number of specimens of this type, and find it to 

 exhibit an enormous range of variation in minor points, such as the number and relative 

 proportions of the cirrhus-segments, the colouring, the presence or absence of a faint 

 keel on the dorsal side of the arms, &c, and am convinced that none of these can be 

 regarded as of specific value. A number of such varieties group themselves around a 



1 Op. tit. p. 104. 2 Op. tit. p. 208. 



3 " Nachtrag zu der Abhandl. iiber die Comatulen," Monatsb. der Berlin. Akad. 1S4G, p. 177. 



4 'Gattuug Comatula,' p. 13. 



