134 Clark — New Genera of Unstalked Crinoids. 



Isometra angustipinna is without doubt the young of Antedon lineata 

 P. H. Carpenter, 1888 (not Antedon lineatus Pomel, 1887), which was 

 renamed challengeri by A. II. Clark in 1907, before its relation to 

 angustipinna was detected. 



Family PEXTAMETROCRIXID.E nom. nov. 

 Pentametrocrinus gen. nov. . 



Eudiocrinus P. H. Carpenter, 1882 (part), but not Ophiocrinus Semper, 



1868 (not Ophiocrinus Salter, 1856). 



Genotype. — Eudiocrinus japonicus P. H. Carpenter, 1882. 



Costals absent, the first post-radial joint being the first brachial; no 

 orals; rive arms. 



Color. — Purplish gray, the disk black. 



Geographic distribution. — Intertropical; West Indies; coasts of south- 

 ern Europe; coast of Somaliland eastward through the Indian Ocean to 

 southern Australia, northward to Japan. 



Depth. — 103 to 1,050 fathoms; mainly abyssal. 



Eudiocrinus was originally differentiated from " Antedon" on account 

 of the possession of five undivided arms; and it seems to have escaped 

 the notice of all subsequent workers on the comatulids that the undivided 

 arms of the Eudiocrinus indivisus type are radically different in structure 

 from those of the Eudiocrinus japonicus type. Eudiocrinus indivisus, E. 

 granuiatus, and E. variegatus (the first the type of the genus) have two 

 costals united by syzygy, as in Zygometra, the genus to which they show 

 the closest affinity; but they differ from Zygometra in that the second 

 costal bears a pinnule instead of an additional arm. The third post-radial 

 joint is the real first brachial, and is joined to the succeeding joint by 

 synarthry, as the first brachial is joined to the second in all comatulids; 

 there is, of course, no pinnule on this joint, as the first brachial never 

 bears a pinnule; the fourth post-radial joint {i.e., second brachial) is 

 joined to the succeeding by an "oblique muscular" articulation, as are 

 all second brachials to succeeding joints; it bears a pinnule on the side 

 opposite to that on which thecostal pinnule is borne, as a synarthrial arti- 

 culation, like its derivative, a syzygy, not only never admits of the devel- 

 opment of a pinnule, hut is non-effective in regard to the pinnule devel- 

 oped on the next oblique muscular articulation, which, therefore, occurs 

 on the same side as it would if the synarthry or syzygy were not there, but 

 the two joints were merely a single joint. A muscular articulation, on 

 the other hand, always affects the position of the next pinnule, no matter 

 whether a pinnule is developed at the articulation or not, causing it to 

 appear on the same side as tin' preceding pinnule ; Perometra and Cyllo- 

 metra and also Erythrometra are examples of this, between the fifth and 

 sixth post-radial joints ( i. e., the third and fourth brachials ) occurs the 

 first syzygy, which, therefore, occupies the same position as in Zygometra 

 and in almost all other comatulids. In "Eudiocrinus " atlanticus, E. 

 japonicus, E. semperi, E. tuberculatum, and 7*-'. varians, as in Decametro- 



