THE BEITISn SECOXDART ROCKS. 51 



4. ACTINOMETRA LoY^^^I, n. Sp. 



This fossil consists of the centrodorsal, radials, and first two 

 brachials of what must have been a large Actinometra. The centro- 

 dorsal is exceedingly peculiar, and but for my experience with the 

 ' Challenger ' Comatulce I should have been greatly puzzled what to 

 make of it. In fact it has been generally taken for the " head " of 

 a Ptntacrinus, to which it has a considerable resemblance, except in 

 the absence of external basals ; and even these pieces seem to be 

 wanting in some species of the genus (P. Fisheri for example) as it 

 is at present constituted. 



Actinometra Loveni, n. sp. From the Gault, Folkestone. 



Dorsal aspect of the calyx, showing the clefts between the first radials and the 

 sides of the centrodorsal, which shows no traces of the attachment of 

 cirrhi. X 2. 



In my preliminary report upon the ' Challenger ' Comatulce'^ I have 

 described how the centrodorsal of some tropical species undergoes 

 a long series of changes in its shape and relations, which do not 

 commence until some time after the loss of the stem and the entry 

 upon a free state of existence. These changes are pf three kinds : — 

 (1) the loss of all the cirrhi and the gradual obliteration of their 

 sockets ', (2) the lowering of the centrodorsal to the level of the 

 radial pentagon, or sometimes even below it ; and (3) the appearance 

 of clefts at its sides between its ventral surface and the dorsal faces 

 of the first radials. These three features are combined in various 

 ways in several tropical Comatulce. The clefts are largest in Act. 

 stellata, Ltk., and in Loven's Phanogenia tijjnca ; but in the former 

 species the centrodorsal is entirely devoid of cirrhi and altogether 

 below the level of the radial pentagon, while in Phanogenia it is a 

 trifle above the level of the radials and bears a few indistinct cirrhus- 

 sockets. Act. Loveni presents a condition intermediate between 

 these two. 



* Proc. E. S., No. 194, pp. 390-393. 



e2 



