NOTES ON GENERA. 123 



arm. Two of the fossil species of Pentagonaster, namely P. lunatus and obtusus, 

 have all arms which are well produced (the arms in the specimen of P. lunatus 

 figured on PI. IV, fig. 1, are broken off short). The third and remaining species, 

 P. quinquelola, is usually much more pentagonal in shape, although a specimen in 

 the possession of Dr. Blackmore has a major radius at least twice the magnitude 

 of that of the minor radius. 



The species assigned to the genus Nympliaster by Sladen were so assigned 

 because their structure and character, so far as they could be made out from the 

 fragmentary condition of the fossils, appeared to warrant their inclusion in the 

 genus Nympliaster (see p. 15). 



It appears to me that these species have the same generalised characters as 

 those assigned to the genera Calliderma and Pentagonaster. The distinctive 

 character of the genus Nympliaster is the possession of paxillae on the abactinal 

 plates. No fossil species is sufficiently well preserved to show whether these were 

 absent or present, and it is impossible therefore to confirm or deny Sladen's 

 suggestion. 



It will be seen from the above that there is no certain evidence which entitles 

 us to distribute the Cretaceous species amongst the three genera, and it may be 

 the task of a future observer to place them in one new genus. I have, however, 

 in order to secure uniformity, utilised all these generic names even for the 

 description of new species. The following species also appear to require revision. 



Calliderma Smithiss, C. mosaicum. 



After examination of the fairly numerous specimens of the fossils assigned to 

 these species in the British Museum (Nat. Hist.) I cannot confirm the specific 

 distinctions made by Sladen on pp. 10 and 11 of this Monograph. All the 

 characters mentioned vary greatly in individual specimens. The ornament, 

 however, is common in character to both species, and I should prefer to unite them 

 in one species, namely, G. Smithiae, as this has prior place in the original account 

 given by Forbes. 



The specimens figured on PI. VII, figs. 1 and 2, and stated by Sladen to be in 

 his opinion doubtful examples of N. Goombii (p. 17), should in my opinion be 

 assigned to C. Smithise, as should also the specimen figured on PI. XIX, fig. 3. 

 These examples possess a finer type of honeycomb structures on their marginalia 

 than is usually met with in C. Smithise, and they may, therefore, be a distinct 

 variety of this species (see Text-fig. 8). 



A specimen preserved in the British Museum (Nat. Hist.) E. 5063, was figured 

 by Sladen on PI. V, fig. 1 a, of this Monograph as Tomidaster sulcatus. Apparently 

 it was the intention of Sladen to make a new genus and species for the reception 



