60 F. A. BATIIEK, CRINOIDEA OF GOTLAND. 



The dorsal cup of Castocrinus consists then of a circlet of 5 radials, of which three 

 are compound; and a circlet of appacently only 4 basals, which alternate with the radials 

 except in the interradius between the two adjacent compound radials. The two larger 

 basals apfpear to meet along this line, as is well secn in the type-speciinen of C. fureil- 

 latus; so that it is from this interradius that the fifth basal is missiug. 



Besides these plates, Dr. Ringu-eberg has described a narrow plate, of irregular 

 four-sided shape, lying between the two distal halves of the adjacent compound radials; 

 and he has ealled it »the azygous plate». This plate has been omitted from the above 

 description for the following reasons. First, mere inspection of Dr. Ringueberg s diagrams 

 (Pl. XI, tig. 1 c, d) shows that this plate plus the upper radial on its left exactly equals 

 the upper radial on its right. Seeondty, this plate has only been described for one speci- 

 men of one species. Thirdly, the original describer, W. R. Billings, omitted all reference 

 to it both in C. fureillatus and C- rugosus. Lastly, I have been unable to discover it 

 either in the type-specimens of C. fureillatus, C. 7'ugosus and C. Billingsianus, inöst 

 kindly lent to me by Mr. W. R. Billings, or in a large and well-preservecl specimen of 

 C. fureillatus (Brit. Mus. E. 6,001) which I have myself prepared with great care. On 

 the contrary, the combined evidence of these and other specimens makes it very clear 

 that what Dr. Ringueberg mistook for a separate plate is merely a portion of the super- 

 radial that supports the anal tube, which portion has been depressed to form a groove 

 for the reception of the steni. In the larger of the two type-specimens of C. Billingsi- 

 anus this groove affects also the first and second plates of the anal tube itself. Even 

 su|jposing that this plate existed, it coukl not, for reasons hereafter given, be »the azygous», 

 as that term has been used by American writers; it could in fäet only be an intercalated 

 plate of temporary importance. 



The next point to deterrnine is the orientation of the cup, and this may be done 

 by both direct and comparative evidence. 



First the direct evidence. Of the two adjacent compound radials, that on the right 

 supports an arm, but that on the left supports a series of plates which form part of the 

 ventral tube. This is a feature as to which there has never been any doubt. Now in all 

 other Inadunata the ventral tube, so far as it is connected with a radius at all, is con- 

 nected with the right rather than with the left posterior radius, as is most clearly seen 

 in Iocrinus and Merocrinas; even Messrs Wachsmuth and Springer will hardly dispute 

 this. It is therefore to be inferred that the radius of Castocrinus in which the ventral 

 tube occurs is the right posterior radius, and so forth as in text-tig. 13 a. 



Secondly, the comparative evidence. If the diagram of Castoerimis be compared 

 with the diagrams of Heterocrinus (text-tig. 6, p. 25) and Ectenocrinus, or with Haplo- 

 crinus (text-tig. 5), it will be seen that in each case there are two simple and three com- 

 pound radials. It is admitted that in Heterocrinus, Ectenocrinus and Haplocrinus the 

 compound radials are the right posterior and the right and left antrrior: and in hardly 

 any Inadunate genus is the left posterior radial ever divided horizontally. We are there- 

 fore bound to suppose that the same is the case with Castocrinus, and thus we arrive at 

 the same conclusion as followed from the direct evidence. The correctness of this view 

 is confirmed by a comparison with other Inadunata, such as Anomalocrinus, Mycocrinus, 



