m 
enlarged beyond strict specific limits. The low calyx, deep ventral concavity, 
into which the basal plates fairly enter, and the diminished scar of the first 
stem-joint, recall the characters of P. nodosus, hut our want of knowledge of 
the latter above the hasi-radial sutures prevents further comparison. 
The most interesting point in the structure of P. Stephensi is the 
relatively small calyx as compared with the preponderating mass composed 
of what I regard, for the want of a better explanation, as the anchylosed first, 
second, and third costals. A glance at PI. XX, Pigs. 1-3, will shoAV that the 
infra-hasals, hasals, and radials compose the saucer-shaped calyx, as in P. 
uocjtis-, whilst in Pig. 8, is visible the anal jdate reposing on the truncated 
basal, as in P. Konincl'l and P. nodosus. So far the structure seems to b-e 
simple enough, and corresponds with its fellow species, but above the radio- 
costal sutures Ave are confronted Avith the heavy, and apparently anchylosed 
mass seen in PI. XX, Pigs. 1-5. 
On the radials are placed fiAm more or less tabular plates, the two 
posterior separated by the impressions of the plates of the ventral tube, and 
Avhich, I presume, represent the fiAm first costals, with aa'cII marked vacuities 
representing the articular surfaces, between tliem and the radials, and again 
betAveen them and the plates above. The latter seem to be the impressions 
of the second and third costals, if the prominent terrace-like ridge miming 
round the specimen represents the sutures between the plates othenA'ise 
anchylosed together. This explanation is advanced tentatively, for at present 
I see no other reading of the structure of this specimen. The long radio- 
costal articular surfaces are similar to those of P. Konincki, and to the 
exposed rays of P. p7'inccps. The inter-costal articulation betAA'een the first 
and second is also similar. 
The question that naturally presents itself to one’s mind is — Do the 
lateral union and consolidation of the costals — presuming the pieces to bo so 
united in the perfect organism, similar to this cast — infer generic distinction, 
the other portions of the calicicular structure being on the same plan ? It 
apjicars to me that the ansAA'^er to this ([ucstion depends on the classificatory 
Avalue placed on the structure of the arm-pieces in a Crinoid generally. 
Amongst the liest characters assigned by Messrs. AXachsmnth and Springer^ 
for generic separation, the construction of the arms is placed last, and may, 
‘ Eevisionof the Palococrinoidca, Pt. I, 1879, p. 21. 
