NOTES ON ECHINODERM MORPHOLOGY. 11 



of the adult. It will be remembered that Ludwig places them 

 in the category of intermediate plates. I think that they may 

 be identified with tolerable certainty in the following species, 

 while there are others in which their presence is less easy to 

 determine. 



Opbioceramis clausa (PI. I, 



fig. 1). 

 Ophioglypha abyssorum. 

 Ophiozona clypeata. 



Opbiorausium scalare. 



J, validum (PI. I, 



fig. 2). 

 Ophiolepis variegata. 



The last species is perhaps out of place in this list. The 

 dorsocentral is surrounded by three alternating rows of plates, 

 all of them about the same size ; and it is a little difficult to 

 decide whether the proximal row should be regarded as under- 

 basals or as the radial primaries. In the latter case the plates 

 of the second row, instead of being basals, would belong to the 

 interbrachial system ; and they may fairly be compared to the 

 interradials of the Palseocrinoidea and of the recent Thau- 

 matocrinus. 



It will be remembered that in the early stages of the devel- 

 opment of a Crinoid two of the first radials are separated from 

 one another by an anal plate, which rests directly on one of the 

 basals. It subsequently becomes lifted out of the calyx and is 

 eventually totally resorbed. But its earlier condition is perma- 

 nent in many Palaeocrinoids such as Hexacrinus and Dicho- 

 crinus; and a possible parallel to it may be found in the 

 Ophiura stuwitzi of Liitken,^ which has six "primary" 

 plates in contact with one another around the dorso-central. 

 Five of these are opposite the arm-bases, and are therefore the 

 radial primaries; while the sixth is interradial and occupies 

 exactly the same relative position as the anal plate of Dicho- 

 crinus and Actiuocrinus. 



In the last-named genus, and in a large number of other 

 Palaeocrinoids such as Platycrinus, Glyptocrinus, and 

 their allies, there are primary interradials all round the calyx, 

 resting upon the upper faces of every two contiguous radials, but 



1 ' Add. ad. hist. Ophiur.,' loc. cit. i, Tab. i, fig. 8 a. 



