V. Botryocrinus. 405 



that the abnormalities are due to recuperation. The right 

 anterior ray has four costals, of which the fourth is axillary : 

 this ray splits into three main branch es, of which the two on 

 the left, i. e. adanal, side spring from an axillary distichal no 

 longer preserved, while that on the right or outer side springs 

 from the axillary costal and is at first sight perfectly normal ; 

 it too, however, gave off, apparently from its most proximal 

 ossicle, a very small arm. Of the anterior and left anterior 

 rays only a very small portion has been exposed ; it is 

 hardly likely that they were perfectly normal, at the same 

 time there is nothing to prove the contrary, and from the 

 broken distal end of the specimen we learn that each sent 

 only two main arms as far as that point. The small arm 

 that is seen issuing from among the branches of the left poster- 

 ior ray and running up the left side of the specimen may 

 proceed either from the right posterior ray or from one of the 

 anterior rays. Now there are certain features in this speci- 

 men that are quite clearly simple individual abnormalities, 

 possibly even due to accident. As regards other aberrant 

 features the irregularity of their occurrence and variations in 

 their structure should convince everyone that they cannot be 

 of specific value. Similar instances of abnormal repetition of 

 the arms are rare: A. von Strombeck* has, however, 

 described and figured some for Encrinus fossilis, Blum., while 

 Mr. W. Batesonf has recently published a careful figure by 

 Mr. Edwin Wilson and a description by Dr. P. H. Carpenter 

 of much the same structure in Antedon bifida, Pennant, sp. 

 ( = A. rosacea, Linck, sp.). It is more to the point that in 

 various American species of Barycrinus the arms " sometimes 

 branch once on the third or fourth plate in some of the rays — 

 but never in the anterior one — and only in one arm to a ray, 

 the other arm always remaining simple" J. As in none of 

 these cases are the essential characters of the species destroyed, 

 I feel justified in supposing that the present specimen is ab- 

 normal only as regards the secondary arm-branching, and that 

 its other characters are those of a species. 



This species resembles B. decadactylus in the presence of 

 pinnules and therein differs from all other known species of 

 Botryocrinus. In the shape of its stem, of its cup, and its 

 ventral sac it also resembles B. decadactylus more nearly than 

 other species. From B. decadactylus it differs in the more 



* " Ueber Missbildungen von Encrinus tiliiformis, Lam.," Palseonto- 

 grapbica, iv. 169-178, pi. xxi., Cassel, 1855. See especially fig. 12. 



t " On some cases of Abnormal Repetition of Parts in Animals," Proc. 

 Zool. Soc. 1890, pp. 579-588, London, Oct. 1890. See fig. 4. 



IW.&S, Rev. I. (101), Proc. 1879, p. 324. 



Ann. & Mag. N. Hist. Ser. 6. Vol. vii. 28 



