THE BRITISH SECONDARY ROCKS. 43 



sockets on its sloping sides, while the whole of its dorsal surface is 

 smooth, without any traces of sockets. Occasionally, however, the 

 centrodoisal is rather more convex, and only its flattened apex is 

 free from cirrhi, though this occupies a relatively larger area than 

 in most Antedons. The distal faces of the radials are nearly or 

 quite parallel to the vertical axis of the calyx, and also nearly or 

 quite as wide at their upper as at their lower ends. The ventral 

 faces, which in Antedon have a steep inward slope, are almost hori- 

 zontal in Actinometra, sloping very gently inwards towards the cen- 

 tral space. Hence the opening of the funnel becomes widely ex- 

 panded, and, when the radial pentagon is viewed from above, little 

 or nothing is seen besides the proper ventral faces of its component 

 radials. All the species of Actinometra which I have examined 

 have smaller muscle-plates than those of any Antedon except A. 

 macrocnema, so that the distal faces of the radials are very low and 

 the muscular fossae quite inconspicuous. They are separated from 

 the ligament-fossae by very prominent ridges, which are either hori- 

 zontal or curved slightly upwards. These start from the sides of 

 the radial, run inwards towards the middle line, and then turn 

 downwards so as to leave between them a wide furrow which gra- 

 dually dies away below, with the disappearance of its bounding ridges. 

 The only Antedon I know which presents features at all resembling 

 these is the anomalous 'Challenger' species from Station 212. The 

 arrangement of the ridges is essentially the same as in Actinometra, 

 though the shape of the distal faces of the radials is somewhat 

 diiferent. No Actinometra has the distinct rim on the ventral side 

 of the opening of the central canal that exists in all Antedons, in 

 which the transverse articular ridge rises up round the opening as a 

 prominent triangular rim. 



There is one singnilar type of fossil Gomatulce, the Jurassic genus 

 Solanocrinus, Goldfuss*", which has been long regarded as distinct 

 from the recent forms, owing to the appearance of basal pieces 

 on the exterior of the calyx. Schliiterf merges Solanocrinus in 

 Antedon ; for he does not regard the difference between the basals 

 of the two types as of generic value. In the first type they are ex- 

 ternal, while in the second they are concealed and metamorphosed 

 into a rosette, having been relatively large and distinct during an 

 earlier stage of development. On this subject Schliiter remarks :— 

 "I have never yet seen this rosette, as basals are present in all the 

 species which I have examined." Here, of course, he means basals 

 like those of Solanocrinus, which appear on the exterior of the calvx 

 between the radials and the centrodorsal. He describes eight new 

 species, five of which are based on the characters of the centrodorsal 

 piece only ; and it is therefore only an assumption on his part that 

 " basalia " were present in those five species. At the time Schliitcr's 

 paper was written this assumption was perfectly justifiable, in fact 

 the only one which could be made under the circumstances. It was 

 based on the fact that the only Comatulce, besides Glenotremites, 

 with interradial grooves on the ventral surface of the centrodorsal 

 * 'Petrefacta Germanise,' i. p. 166. t Op. cit. pp. 36, 49. 



