226 iMessrs. R. Etheridge, Jiin., and P. H. Carpenter on 



Genus Pii.i:no«chisma, gen. nov. 



Gen. char. Calyx elongately clavate or obclavate ; the 

 number and disposition of the plates and general composition 

 of the ambulacra similar to those of Pentremites. The oral 

 plates are very small, inconspicuous, and always confined to 

 the summit, where they arc either horizontally placed or in- 

 clined inwards. The radials bear three more or less distinct 

 folds diverging from the lips ; and the two contiguous limbs 

 forming the anal side are more or less abortive. Radial 

 sinuses Avide and deep, generally with steep sides. Spiracles 

 as distinct apertures absent, the hydrospires opening externally 

 by a series of elongated slits with intervening ridges, distri- 

 buted in subparallel series on the sloping sides of all the 

 radial sinuses ; they are either both radial and oral or only 

 radial in composition ; and being only partially covered by the 

 ambulacral plates, their distal ends (or even the entire length 

 of some) are visible on the sides of the radial sinuses. Lancet- 

 plate concealed by the side plates (in all but one species) ; 

 outer side plates very small. Anus a separate 0])ening, and 

 further removed from the summit-centre than in Pentrcrnik\s. 

 Column, when compared with the size of the calyx, larger 

 than in the last-named genus. 



Ohii. We have established PhcenoscMsma for a small num- 

 ber of interesting species hitherto included in Pentremites. 

 The late Mr. E. Billings, in a remarkable article " On the 

 8trucrure of the Crinoidea, Cystoidca, and Blastoidea " *, 

 referred as follows to the peculiar structure of the ambulacra 

 in Pentremites caryojyhyllatuSj de Koninckf : — ^' The ends of 

 the fissures of the hydrospires are seen along the sides of the 

 angular ridges, which extend from the apices of the pyramids:): 

 to the angles between the arms. I do not think that such 

 species can be referred to Pentremites ; and if I had specimens 

 before me instead of figures only, I would most probably in- 

 stitute a new genus for their rece])tion." 



It affords us much pleasure to adopt the suggestion of Mr. 

 Billings by proposing the name PhcenoscMsma for Blastoids 

 possessing these characters. They differ from Petitrenn'tes in 

 four essential points of structure — the absence of true spi- 

 racles around the peristome, the presence of a distinct anal 



* Anier. Jouni. Sc. 18G9, xlviii. p. SO. 



t Billings seems to have merely copietl De Ivmiinck's %iiie of tliis 

 species (I.e. p. 79, fig. 11 >, "whicli is eiroueous iii that the direction of 

 the^e tissures is given from below the ambulacra outAvartls, whereas in 

 reality they are subparallel to the latter (see ' Crinoides du Terr. Carb. 

 Belgique/ i8'j4, t. 7. f. o, 5). 



X I.e. the oral plates ( = deltoids of uuthurs). 



