22 THE VOYAGE OF H.M.S. CHALLENGER. 



rays of the basal star, the relations of which are described at length in my memoir on 

 Actinometra. 1 At the time this was written (1877) I had only been able to dissect the 

 calyx in a comparatively small number of Comatulse ; but a detailed examination of the 

 large amount of duplicate material obtained by the Challenger has shown that a basal 

 star is nearly always present both in Antedon and in Actinometra, so that species like 

 Anteclon tenella, Antedon hageni, Antedon phalangium, and Antedon rosacea, in which 

 it is not developed, are the exception rather than the rule ; while there may be traces of 

 it in some varieties of Antedon eschrichti, though not in others. 



It occasionally happens that the rays of the basal star, or, more shortly, "the basal 

 rays," appear on the exterior of the calyx between the centro-dorsal and the first radials. 

 But there is no constancy about this character, even in individual species. Thus, for 

 example, a basal ray is visible in the dissected calyx of Antedon antarctica shown on 

 PI. I. fig. 6a, but there is no trace of it in either of the three specimens figured on 

 PL XXV. figs. 10-12. The basal rays sometimes appear externally beneath the alternate 

 radials of the ten-rayed Promachocrinus (PI. I. figs, la, lc), but this is not always the case. 

 I have also seen them in some individuals of Antedon carinata, though not in that shown 

 on PI. III. fig. la. They are generally to be seen in Antedon macronema (PI. IV. fig. 3a; 

 PI. XXXVIII. fig. 5), in Antedon longicirra (PL XVII.), and also in Actinometra 

 pulchella (PL IV. fig. 5c), and Actinometra stelligera (PL V. fig. 5b) ; while there are 

 other species, such as Actinometra rnaculata and Actinometra lineata, in which they are 

 only occasionally visible. 



I have shown elsewhere that the basal rays have an entirely different origin from 

 either the primary or the secondary portions of the rosette. They are tertiary structures 

 formed by calcification in the synostosis between centro-dorsal and radials. Sometimes, 

 however, they are very substantial structures, and each of them becomes so firmly united 

 with an interradial portion of the rosette that it is often possible to get the entire complex 

 structure thus formed to break up into five separate parts, each representing one basal 

 plate. The results of this operation are seen in Antedon antarctica (PL I. fig. 7), 

 Antedon carinata (PL III. figs, lc, 2a, 2b, 3a, 3b), Actinometra nieridionalis, Actinometra 

 pulchella, and Actinometra paucicirra (PL IV. figs. 4b, 5a, 6b). Each of the compound 

 basals so isolated is a somewhat elaborate structure. The basal ray may be long and 

 narrow as in Actinometra nieridionalis (PL IV. fig. 4b), or short and stout as in Antedon 

 antarctica (PL I. fig. 7) and Actinometra paucicirra (PL IV. fig. 6b.) 



At the proximal end of the basal ray are two openings, one on each side, which give 

 passage to the secondary basal cords ; and they are separated, when seen from the dorsal 

 side, by the interradial process of the rosette with portions of the basal bridge (PL IV. 

 figs. 4b, 6b, yS). The lateral boundaries of these openings are formed by the halves of two 

 of the radial spouts of the rosette which extend outwards from the base of the interradial 



1 Trans. Linn. Soc. Lond. (Zool.), 1879, ser. 2, vol. ii. pp. 95-100. 



