Terms in Crinoid Morphology. 63 
Why should not all interradial plates below the free arms, 
except of course the basals, be called Interbrachials, each row 
being distinguished as first, second, third, &e.? Thus the 
plates to which the term “ Interradial ” is now often wrongly 
restricted would be called “ the first Interbrachials,” or, when 
they alone existed in the dorsal cup, simply “the Inter- 
brachials ” (cbr). 
It would be convenient still to distinguish the corresponding 
plates of the ventral surface as ‘ Interambulacrals ” (¢amb). 
Interradial Plates.—Deltoids. 
In the genus Huspirocrinus there occur on the oral surface 
four cordiform or subtriangular plates. One of these is 
situated in each interradius, except the posterior interradius, 
and abuts on the upturned portions of the radials, ¢. e. on the 
radial processes. ‘These four plates meet one another late- 
rally, beneath the ambulacra, except in the posterior inter- 
radius. In the posterior interradius there is a larger plate of 
somewhat similar shape, which has an irregular surface. 
This plate bears to the peristome the same relation as do the 
four cordiform plates ; it also partly supports the ambulaera ; 
it does not, however, bear the same relation to the radials, as 
it is separated from them by a varying number of plates con- 
nected with the anal tube. One or more of these latter plates, 
on either side of the anal tube, meet the adjacent cordiform, 
plate beneath the ambulacrum. 
The four cordiform plates are also met with in Gissoerinus 
Cyathocrinus, Carabocrinus, Streptocrinus, and other Inadu- 
nate genera. ‘The posterior plate with an irregular surface is 
usually conspicuous in the same genera, The homologies of 
these plates with plates occurring in the tegmen of other 
Crinoids are still in dispute; it is therefore advisable to give 
to them some names that shall not have too great morpho- 
logical significance. 
The posterior plate appears to have been perforated by one 
or more pores, being in some cases quite cribriform *, and it 
is probable that it subserved the functions of a madreporite, 
whatever those functions may be. It will therefore be con- 
venient to apply to this plate the term “ Madreporite,” which 
term, it should be remembered, has no strict morphological 
significance, since the position of the madreporite in other 
Echinoderms is by no means constant. 
‘The four corditorm plates have often been regarded as orals, 
: : Senay eal < : : as 
* Wachsmuth and Springer, “ Perisomic Plates,” Joc. cit. p. 358. 
