Vol. XXVI, pp. 141-144 June 30, 1913 



PROCEEDINGS 



OF THE 



BIOLOGICAL SOCIETY OF WASHINGTON 



a revision of the crinoid family mariame- 



trid.t:. 



BY AUSTIN HOBART CLARK. 



At the present time.theendocyclic comatulids possessing more 



than ten arms in which all the division series consist of two 

 ossicles, the enter cirrus segments bear single median dorsal 

 processes, and the enlarged proximal pinnules are flagellate, at 

 least distally, are distributed among the genera Pontiometra 

 (included in the family Pontiometridfe), Oxymetm (of which 

 the genus St lenemetrn is a synonym ), Mm iametrn and Dirhrometra 

 (included in the family Mariametridse). In addition to the 

 genus Pontiometra the family Pontiometridee contains only the 

 highly aberrant genus Epimetra. 



The family Pontiometridse was originally differentiated from 

 the family Mariametridse on the ground of certain striking- 

 morphological peculiarities which 1 am now led to believe are 

 of purely secondary systematic importance. 



At the time of its description the genus Epimetra was pro- 

 visionally associated with Pontiometra in the family Pontiome- 

 tridse on account of the strong general resemblance of the two 

 types. A closer study of this genus indicates that it should 

 properly he referred to the family Colobometridffi and placed 

 mar the genus Oi/llometra, the grounds upon which this disposi- 

 tion is suggested being (1) the deficient pinnulation, (2) the 

 lateral broadening of the dorsal processes on the outermost 

 cirrus segments (including the broadly bifurcate opposing 

 Spine), and (3) the close correspondence of the details of the 

 arm structure. 



Of the genera Pontiometra, Oxymetra, Mariametra and Dichro- 

 metra, winch together form a perfectly natural family, the 

 35— Proc. Biol. Soc. Wash.. Vol. XXVI. 1913. (Ml) 



