1879.] NATURAL SCIENCES OP PHILADELPHIA. 351 



defined. The ventral sac, which really presents the best generic 

 characters, and by which it is easily recognized, was altogether 

 unknown, and the difficulty was increased when several species 

 were admitted which belong to other groups, and which were evi 

 dently not intended to be included by the authors of the genus. 

 We have been obliged to throw out all species with long, angular, 

 zigzag arm-joints ; these have also a tubular ventral sac, and we 

 have placed them under some of the varieties of Poteriocrinns, 

 where they really belong. 



Zeacrinus has by most authors been placed under Poteriocrinus 

 as a subgenus, but in this we cannot concur. We look upon it 

 rather as the type of an independent little group of Crinoids, in- 

 cluding several genera, which culminates in Hydreionocrinus and 

 Cceliocrinus, some of the last survivors of the Cyathocrinidae. 



Zeacrinus excavatus Schultze is evidently a Taxocrinus. 



Geological position, etc. The genus is confined to the Subcar- 

 boniferous, ranging through all the divisions of that epoch; and 

 has only been discovered in America. 



We recognize the following species : 



1869. Zeacrinus asper Meek and Worthen. Proc. Acad. Nat. Sci. Phila,, p. 150. 



Geol. Rep. 111., vol. v. p. 430, pi. 1, fig. 7. Lower Burlington limest. (not 



Upper Burlington 1. as stated by M. and W.). Subcarb. Burlington, Iowa. 

 1859. Zeacr. bifurcatus McChesney. New Pal. Foss., p. 10. Trans. Chicago 



Acad., 1867, vol. i. p. 71, pi. 4, fig. 3. Chester limest. Subcarb. Chester, 111. 

 *1862. Zeacr. bursaeformis White. (Poteriocr. bursaeformis.) Proc. Bost. Soc. 



Nat. Hist. , p. 10. Lower Burlington limest. Subcarb. Burlington, Iowa. 

 1873. Zeacr. compactilis Worthen. Geol. Rep. 111., vol. v. p. 536, pi. 21, fig. 5. 



Subcnrb. Cumberland Co., Ky. 

 1858. Zeacr. elegans Hall. Geol. Rep. Iowa, vol. i. pt. ii. p. 547, pi. 9, figs. 1 and 



2. Upper Burlington limest. Subcarb. Burlington, Iowa. 

 1847. (1) Zeacr. fiorealis Yandell and Shumard. (Cyathocr. florealis.) Cont. 



Geol. Kentucky, p. 24, pi. 1, fig. 1. Shumard, 1855. Poteriocr. florealis, 



Second Rep. Geol. Missouri, pi. ii. p. 217. Shumard, 1866. Zeacr. florealis. 



Cat. Pal. Foss., pt. i., Echinodermnta, p. 399. Chester limest. Subcarb. 



Grayson Co., Ky. 



We are not certain that this species belongs here, as we have 

 never seen the description. 



1858. Zeacr. intermedius Hall. Geol. Rep. Iowa, vol. i. pt. ii. p. 681, pi. 25, fig. 

 4. Chester limest. Subcarb. Chester, III. 



1846. Zeacr. magnoliaeformis Owen and Norwood. Type of the genus. (Cya- 

 thocr. magnoliaeformis.) Research Pot. Carb. Rocks, Kentucky. Troost, 

 1850. Zeacr. magnoliceformis. Cat. Crin. Tenn. Hull, 1858, Geol. Rep. 

 Iowa, vol. i. pt. ii. p. 543 and 684, pi. 25, fig. 4. Chester limest. Subcarb. 

 Grayson Co., Ky. 



