442 MR. p. H. CAUPEKTEB ON THE GENUS ACTINOMETRA, 



while in the other there are five, the mouth being excentric in both 

 cases. 



These and^many similar instances have led the author to the con- 

 clusion that the real distinction between Antedon and Actinometra 

 lies in the subcentral or excentric position of the mouth, and that 

 the number of groove-trunks reaching the peristom is a character of 

 very minor importance. The definition of Actinometra, therefore, 

 will have to be extended so as to include those forms in which 

 there are five or more primary groove-trunks, as well as those 

 forms with less than five, for which the name was originally in- 

 troduced by Miiller. 



After arriving at the above conclusion, the author learnt from 

 Dr. Liitken, of Copenhagen, that he had held similar views for some 

 time past. Dr. Liitken further informed the author that Antedon 

 and Actinometra also differ from one another in the character 

 of their oral pinnules. In the former genus, with the mouth sub- 

 central, the oral pinnules are but slightly difierentiated from those 

 of the rest of the arm, while in Actinometra they are always very 

 different from the others, being more or less flagelliform with 

 small lateral shield-shaped processes on their terminal joints, which 

 thus have a comb-like appearance. 



Although, like Dr. Liitken, the author has found that in all the 

 ComatulcB he has examined the terminal comb on the oral pin- 

 nules invariably coexists with an excentric mouth, and is absent 

 in those forms with a subcentral mouth, yet this does not seem 

 always to be the case ; for Loven* has described a new Comatula 

 under the name of PTianogenia, in which the mouth is central, but 

 the oral pinnules have a terminal comb. 



This form is perhaps generically distinct from Antedon and 

 Actinometra, as it presents some peculiarities in the structure of 

 the skeleton ; but in a new American species described by Pour- 

 talest this is not the case, and the mouth is excentric, while the 

 oral pinnules are not specially distinguished : the same appears 

 to be the case in the Comatula rosea of Miiller ; and the author is 

 therefore not disposed to attach very much importance to the pre- 

 sence or absence of a terminal comb on the oral pinnules as a 



,* Pbanogenia, ett hittills okandt slagte af fria Criuoideer. Ofversigt af 

 Kongl. Vetenskaps-Akademiens Forhandlingar, 1866, No. 9, pp. 223-233. 



t " List of the Crinoids obtained on the coasts of Florida and Cuba, by the 

 United-States Coast-Survey Gulf-Stream Expeditions, in 1867, 1868, 1869 " 

 (' Bulletins of the Museum of Comparative Zoologj',' Cambridge, U.S., No. 11), 



