76 ME. P. H. CAEPENTEE ON THE GEM US ACTINOMETEA. 



rosette or metamorphosed basals, differs in many points from that of Ant. rosacea and 

 of all the other species of Antedon which I have examined. 



In all of these the external or distal faces of the first radials slope at a considerahle 

 angle from above and within downwards and outwards, so that a view of the upper or 

 ventral aspect of the radial pentagon formed by their union (PI. IV. figs. 4, 17) shows, 

 not only their small superior or ventral faces around the central funnel-shaped space (F), 

 but also the greater part of their inclined external faces (PI. IV. figs. 6, 8, 14), viz. the 

 fossae (/) for the attachment of the muscles between the first and second radials (PI. IV. 

 fig. 5, r.m) and the smaller ones (/*) which lodge the interarticular ligaments, the distal 

 opening of the central canal (c.c), and the large transverse articular ridge (i), together 

 with more or less of the large fossa (/) which lodges the elastic ligament. The amount 

 of this fossa which is visible on the ventral aspect of the radial pentagon varies in 

 different cases. 



In correspondence with this inclination of the distal faces of the first radials of Antedon 

 to the vertical or dorsoventral axis of the calyx, their ventral faces are much reduced and 

 are very small in comparison with the dorsal ones. 



When the ventral surface of an isolated first radial of Ant. rosacea is examined (PI. IV. 

 fig. 12 a), it is seen to be divided into a central and a peripheral portion by two curved 

 ridges, bending towards each other along the median line, and there separated by a 

 furrow (fj). The central portion only is the true ventral face of the radial. It slopes 

 inwards, so as to contribute to the formation of the central funnel-shaped space (PI. IV. 

 fig. 17, F) occupying the centre of the radial pentagon, and partially filled up by a cal- 

 careous network formed by the inosculation of processes which proceed from the internal 

 and ventral faces of the surrounding radials (PI. IV. fig. 12 a, en). The peripheral 

 portion, on the other hand, slopes outwards, and is, in fact, the upper or ventral half of 

 the inclined external face (fig. 14), namely, the large vertical lamella? in which the mus- 

 cular fossa? are excavated. The upper and inner edges of these lamella? form the curved 

 ridges above mentioned, each of which has two limbs, one superior (fig. 12 a, g^), which is 

 horizontal, or nearly so, and forms the external boundary of the ventral face, and one 

 inferior (g 2 ), which descends along the median line of the inclined external face towards 

 the great transverse articular ridge (i) ; it is separated from the corresponding inner 

 edge of the other muscular fossa by the furrow (/J, which may therefore be called 

 " intermuscular." 



These curved ridges thus produce great inequalities in the ventral aspect of the 

 radial pentagon (PL IV. fig. 17). The walls of its central funnel present an alternation 

 of radiating ridges and furrows, of each of which there are ten. Five of the furrows 

 (v.i.f) correspond Avith the divisions between the component pieces, and are therefore 

 interradial, while the ridges which bound them are the superior limbs (#,) of the curved 

 ridges above mentioned, one belonging to each of the two contiguous radials. Of the 

 other five furrows, one passes along the middle of each of the five radials, and both the 

 ridges which bound it belong to the same piece — being, in fact, the median or descending 

 margins (g 2 ) of the large vertical lamella? in which the muscular fossa? (f) are excavated. 

 These furrows, therefore, are simply the intermuscular furrows of the distal faces (PL IV. 



