71 ME. P. H. CAEPENTEE ON THE GENUS ACTINOMETEA. 



That Glenotremites is the centrodorsal piece of a Com a tula there can, I think, he little 

 donht ; hnt I see no reason to regard the central opening as a mouth, any more than in 

 any other of the centrodorsal pieces represented in Plates IV., V., and VI. In all these 

 cases the centrodorsal cavity, as we know from Gotte's observations, is derived from the 

 posterior part of the right peritoneal diverticulum of the larval alimentary canal, and 

 is therefore a part of the general body-cavity or enteroccel. It is occupied by the dorsal 

 half of the quinquelocular organ which rises through its central opening, the so-called 

 mouth of Glenotremites, and is continued as the "axial prolongation" (PI. VIII. 

 fig. 3, a.p) through the central aperture of the rosette upwards into the middle of the 

 visceral mass. 



In Ant. rosacea this central opening is surrounded by five depressions (PL IV. fig. 15, q), 

 which are the dorsal terminations of the five radial diverticula of the body-cavity en- 

 closed between the radial spout-like processes of the rosette and the internal faces of the 

 first radials. These diverticula exist both in Antedon and in Actinometra (PL VIII. 

 fig. 3, a.r.c), but do not always reach the ventral surface of the centrodorsal piece as in 

 Ant. rosacea (PL IV. fig. 15). If we suppose the above-mentioned depressions (5) placed 

 radially around the centre of this surface to be deepened sufficiently to become openings 

 leading into the centrodorsal cavity, they would occupy precisely the same position as 

 the so-called genital openings J of Glenotremites ; and simply effect a more open com- 

 munication between the two parts of the coelom contained in the centrodorsal piece on 

 the one hand, and the general cavity of the calyx on the other, than when the ventral 

 surface of the former presents only a single central opening, as in Antedon and Acti- 

 nometra. 



If the view advanced above be correct, it follows that the peripheral part of the areas 

 around the " genital openings " of Glenotremites are the representatives of the radial 



1 These so-called " genital openings " were described by Goldfuss as " Locher." Schliiter, however, merely speaks 

 of them as " Gruben " (pp. 33, 42), and uses the same term for the whole cavity of the centrodorsal piece, " welche das 

 Herz (??) oder gekammerte Organ aufnimmt," and is therefore spoken of by him as the " Herzgrube." But from 

 his expressions, " centralo Herzgrube fiinfseitig " or " zehnseitig," he obviously intends "Herzgrube" to mean nothing 

 more than the central opening of the ventral surface of the centrodorsal, which he elsewhere calls the " Nahrungs- 

 canal " (!), although he evidently understands its real meaning. 



I cannot therefore clearly make out from Schluter's paper whether the " Eadialgruben " are real perforations or 

 mere depressions, as in Ant. rosacea, which, by-the-bye, is the same species as the Antedon europceus of Greeff, and 

 not different from it as Schliiter seems to think. His figures (pi. i. figs. 1, 4, & 10, and pi. ii. figs. 1 & 3) appear to 

 represent ventral openings in the centrodorsal of some fossil Anteclons, just as described by Goldfuss in Glenotremites ; 

 but then he refers (p. 33) to Ludwig and Greeif (!) as describing the radial pits of Ant. rosacea as " sackforrnige, in 

 den Kalkseheitel eindringende blindgeschhssene Erweiterungcn der Leibeshohle." 



His use of the word " blindgcschlossene " would seem to indicate that the " Eadialgruben " of his specimens are 

 really pits, closed below as in Ant. rosacea, and not actual openings; for in the latter case these extensions of the 

 ccelom contained within the radial axial canals would have opened into the centrodorsal cavity (also a part of the 

 coelom), i.e. into that part of it which was not filled up by the chambered organ, and they could not then be accu- 

 rately described as " blind.'' The " Eadialgruben " seem, however, to have been actual perforations in Ant. semi- 

 ghoosus (Sehl. pi. i. fig. 10); for Schliiter speaks of them (p. 42) as " mit der Centralgrube verschmolzen (reiehen 

 aber tiefer hinab)," though he suggests the possibility of this being due to an accidental fracture of their central bony 

 border. The point is one of some interest ; for in no recent Comatula yet known are the "Eadialgruben" more than 

 simple pits, such as arc generally found in Ant. rosacea. 



