18 MB. P. H. CARPENTER ON THE GENUS ACTINOMETRA. 



either six or seven. In no case are there only five with their branches so regularly 

 distributed as Midler figured them in Alecto multiradiata (PL I. fig. 4) ; nor in the single 

 individual with only four primary trunks (fig. 15) is the distribution so regular and 

 symmetrical as in Midler's figure of Actmometra WahlbergMi (fig. 3). Farther, the dis- 

 tribution of the ambulacra on the disk of the specimen of Act. Solaris, represented in 

 PI. I. fig. 5, is by no means so symmetrical as Miiller found it to be in the large Vienna 

 specimen wbich he made the type of his new genus Actmometra (fig. 2). It can hardly 

 be said of fig. 5 that the " Furchen der zehn Arms miinden in gleichen Abstiinden in 

 eine die Scbeibe umziehende Cirkelt'urche." 



The above instances, which could be multiplied indefinitely, suffice to show the 

 impossibility of classifying the Comatulce according to the distribution of the ambulacra 

 on the disk. We have already seen (sect. 9) that Miiller found the Lund and Paris 

 specimens of his species Com. multiradiata to agree in every respect but this ; so that, had 

 he adhered strictly to his own system of classification, he would have had to refer the 

 former to Actinometra and the latter to Alecto. In this case, however, as in all the 

 specimens represented (PL I. figs. 2-16), there is one point of agreement, viz. the relative 

 positions of the mouth and anal tube. In the Paris, Bonn (fig. 4), and Lund specimens 

 of C. multiradiata, Mull., in both the specimens of Act. Solaris, represented in PL I. 

 figs. 2, 5, in A. Walhberghii (fig. 3), and, lastly, in all the eleven specimens of A.polymorpha 

 (figs. 0-16), the centre of the disk is occupied by the anal tube, and the mouth is situated 

 excentrically, either close to the margin of the disk (fig. 11), or at some point rather 

 nearer to the centre. 



(§ 14) After arriving at the conclusion that in this character, the central or excentric 

 position of the mouth, lies the real distinction between Antedon and Actinometra, and 

 that the number of groove-trunks reaching the peristome is a character of very minor 

 importance, I wrote to Dr. Liitken, of the University Museum, Copenhagen, upon the 

 subject, and was not surprised to learn that he had held this opinion for some time past. 

 With his usual kindness he has permitted me to make use of the following extract from 

 an unpublished MS. of his, containing descriptions of some new species of recent 

 Comatulce : — 



" One of the reasons why it is so difficult to identify Midler's species is, that he does 

 not always mention the positions of the mouth and anal tube, and the direction of the 

 ambulacra on the disk, but has evidently established a somewhat unnatural distinction 

 between the differences which may occur in these characters. Two cases may occur : in 

 the one the mouth is subcentral (' quite central ' probably never occurs), and the ambu- 

 lacral farrows convennni? from the arms unite into five trunks, which all run directlv 

 towards the mouth along the shortest line ; they differ, therefore, but slightly in length ; 

 and the ' interpalmar ' areas defined by them are of almost ecmal size, that containing 

 the anal tube having sometimes, however, a slight preponderance in size, especially when 

 the anal tube is placed close to the mouth, almost centrally. In the other case the 

 mouth is removed towards the margin of the disk ; and of the ambulacra, those only which 

 come from the arms nearest to the mouth run directly towards that orifice, while the 

 others, and especially the two enclosing the anal area, are obliged to make a large 



