1879.] the Comatulae of the " Challenger" Expedition. 389 



anything like the relative size of the reniform plates at the sides of 

 the grooves of Rhizocrinus, Hyocrinus, and Bathycrinus. They are all 

 folded down more or less completely over the grooves, which are thus 

 converted into tnnnels ; while the month is also rendered more or less 

 invisible by the folding over it of the plated leaflets aronnd the edges 

 of the peristome. The closnre of the grooves is mnch more perfect 

 in some specimens than in others and may extend far out on to the 

 arms. 



The plates in the marginal leaflets are probably moveable as the 

 nnplated leaflets are in Antedon rosacea ; so that they can be erected 

 when the arms are spread ont, leaving the grooves open for food 

 particles to travel towards the month. On the other hand, when the 

 arms are all contracted over the disk, the marginal plates fold over 

 the grooves and cover them in. This is the condition of most spirit- 

 specimens, but it is not in any way comparable to that of the 

 Palaeozoic Crinoids, in which the month is truly subtegminal, while 

 the ambulacra become real tunnels beneath the upper surface of the 

 vault. 



Sections through one of these plated Hyponome-disks show that all 

 the various structures which underlie the grooves of ordinary 

 Comatulai are present and exhibit their usual characters. 



A new Comatula has been described by Loven* under the name 

 Phanogenia, which presents a very remarkable condition of the centro- 

 dorsal piece. 



Loven's specific diagnosis of Phanogenia typica commences as follows : 

 — " Calyx fere planus, facie dorsali totus cum brachiis Icevis, suturis line- 

 aribus, facie ventrali usque ad finem brachialis secundi sulcis aratus, 

 quibus adhaeret perisoma. Articulus centrodorsalis, verticillaris, per- 

 sistens, simplex-, formam servans stellar quinquangularis minutai, sinubus 

 rotundatis, radiis obtusis, facie dorsali leviter convexa Icevis, cirris prca- 

 ditus perpaucis {circ. octo. ?), in sinubus sparsis, pusillis, quint em partem 

 diametri stelloe longitudine vix superantibus, crassiusculis, versus basin 

 validiusculis, teretibus, leviter arcuatis, Icevibus, apice muticis, caducis 

 foveolas relinquentibus minutas medio per for at as." The figure accom- 

 panying the above description shows the centrodorsal in the form of a 

 five-rayed star, which does not, however, spread out over the radials so 

 as to conceal them more or less completely, as is usual in most Coma- 

 tulae, except that the points of the star just overlie the inner ends of 

 the lines of synostosis of every two adjacent radials. The dorsal 

 surface of the star is level with that of the rest of the calyx, and is 

 marked by a few cirrhus sockets, in two or three of which there are 

 one or two very minute cirrhus stumps. 



This is a very remarkable condition of the centrodorsal. In nearly 



* "Phanogenia, ett hittills okandt slagte af fria Crinoideer." " Ofversigt af 

 Kongl. Yetenskaps-Akademiens Forhandlingar." 1866. No. 9. 



