BATOCEINID^. 485 



at the outer surface. The pinnules form a longitudinal roll along the sides 

 of each arm; they are closely packed, and their ends infold over the food 

 grooves from the sides. In the fossil state the dorsal surfaces of the pin- 

 nules are exposed to view, but in the living crinoid they evidently were 

 capable of straightening out to expose their ventral surfaces, and to open the 

 food groves of the arms to the water. The pinnules are composed of very 

 deep, elongate joints ; they are contiguous at their proximal ends, and so 

 regularly arranged that it appears as if they might have been connected 

 laterally for a part of their length, only the upper parts being movable. In- 

 terbrachials one ; large ; followed by two smaller ones, which meet with the 

 plates of the disk. The anal plate rests upon two basals; it is nine-sided, and 

 succeeded by three and two plates. Of the construction of the tegmen very 

 little is known, it being generally concealed by the lower pinnules ; but 

 from appearances it was composed of large, subspinous orals, asymmetrically 

 arranged, which alternated with five similar jjhites evidently representing 

 radial dome plates. Anus excentric, opening directly through the disk. 

 Column stout, circular. 



Disfribution. — Restricted to the Upper Silurian, and hitherto recognized 

 only in Gotland, Sweden. 



Ti/pe of the genus : Barrandeocrmus sceptrum Angelin. 



Remarks. — Through the kindness of Di-. G. LindstrOm and the great skill 

 and intelligence of Mr. Liljevall, we were enabled to procure a series of draw- 

 ings made from specimens in the National Museum at Stockholm, by means 

 of which the details of structure of this extraordinary Crinoid are shown very 

 completely. (Plate VIII., Fig 1.) Although superficially presenting unique 

 chai'acters, it is a true Batocrinoid, and we find no necessity of recognizing 

 for this genus a distinct family. The recumbent arm feature is found among 

 the Hexacrinidse, and also in one species of the Acrocrinidte, in which it is 

 as marked a character as in Barrandeocrinus, but in Acrocrinus and the other 

 forms with recumbent arms — except Bmrandeocrinus — the pinnules are 

 stretched out, and their ventral surfaces are exposed instead of being folded 

 over the ventral surface of the arm. 



Our generic description was made to agree with the Swedish form, and 

 may have to be slightly modified should additional species be discovered 

 hereafter. It is possible that the specimen figured and described by S. A. 

 Miller in the 18th Report of the Indiana Geological Survey, p. 31, Plate 5, 

 Figs. 13 and 14, under Ct/licocrinus canalicidatiis may belong to this genus. 



