ME. P. H. CAEPEMER ON THE GENUS ACTINOJIETRA. 91 



oiDcnings of spaces between tlie successive segments, which are similarly situated, with 

 regard to the radial symmetry of the animal, to the radial spaces in Act.pectinata, viz., 

 in the direction of the radii ; and they are produced in the same way, by the apposition 

 of two grooves radiating outwards from the centre of each stem-segment, which are 

 largest at their central ends and shallowest towards the periphery. 



(§ 62) In Ant. rosacea and celtica{l^\. IV. figs. 3, 7, 16), and in Act. rohusta and Solaris 

 (PL V. figs. 3, 10, 12, 13), the sides of the interradiai furrows (d.i.f) on the dorsal surface 

 of the radial pentagon are simple and straight ; but in Act. pectinata that portion of the 

 dorsal surface of each first radial which is next to its truncated lateral edge is raised 

 into a sort of curved ridge or fold (PI. V. fig. 12 b, b.f), so that in the natural con- 

 dition of mutual apposition of the five first radials the dorsal interradiai furrows become 

 somewhat lancet-shaped. They correspond in position with the basal grooves on the 

 ventral surface of the subjacent centrodorsal piece (PL V. fig. 7, h.g), and in the cavity 

 formed by the apposition of the edges of these two grooves lie, as will be subsequently 

 seeii, the five rays of the basal star. 



The fi.rst radials of Act. polymorpha are very similar to those of Act. pectinata. Those 

 of variety 1 (PL VI. fig. 12) are like those of the type (PL VII. fig. 1), except in the 

 simpler condition of their ventral surface, which is far less marked by secondary ridges 

 and furrows than is the case in the type (PL VI. fig. 5). In the other three varieties, 

 the first radials of which resemble one another very closely, this sculpturing of the 

 ventral surface is even more marked than in the type (PL VI. fig. 23 ; PL VII. fig. 4 c). 

 The angle between the dorsal and internal faces is considerably less in the type 

 (PL VII. fig. 1 a,d) and in var. 1 than in varieties 2, 3, and 4, the first of which 

 resembles Act. pectinata in the presence of a median depression of the dorsal face 

 (PL VII. fig. 4 a,d, d.r.f), which corresponds with a similar depression along the 

 median line of the radial areas of the small centrodorsal piece (PL VI. fig. 17, r.ar). 

 This dorsal interradiai furrow does not exist in varieties 3 and 4, nor in var. 1 (fig. 13), 

 while there is a trace of it in some specimens of the type, but not in others (figs. 4, 9). 

 In like manner the development of the openings of the radial axial canals on the 

 dorsal surface of the pentagonal base, which are so large in Ant. rosacea and in Act. 

 robusta (PL IV. fig. 16 ; PL V. fig. 12, Q), is in Act. 'polymorpha extremely variable. In 

 tAvo specimens of the type (PL VI. figs. 4, 11) they are entirely absent, as in Act. 

 Solaris (PL V. fig. 3) ; in another the inner margin of the dorsal face of each first radial 

 exhibits a slight median notch (PL VI. fig. 9 ; PL VII. fig. 1 a, Q'), which would be 

 completed into an opening by the apposition to it of the end of one of the radial 

 spout-like processes of the rosette. 



In variety 1 this notch is fairly marked, and five small openings are consequently 

 visible around the central vacuity, on the dorsal surface of the pentagonal base (PL VI. 

 fig. 10, Q). In varieties 2 (PL VII. fig. 4 a) and 3 it is somewhat more distinct ; and 

 in var. 4 it exists in. three of the first radials, but not in the other two, so that there 

 arc only three openings on the dorsal surface of the pentagonal base (PL VI. fig. 21, Q). 



The extent to which the basal folds are developed at the sides of the dorsal inter- 

 radiai furrows is also very variable in Act. polymorpha. We have seen that, although 



SECOND SEMES. — ZOOLOGTf, VOL. II. 13 



