UINTACRINUS: ITS STRUCTUEE AND EELATIONS. 47 



not been fully observed, yet from specimens before him he believes he can 

 safely venture to assume that it was covered with moderately large, toler- 

 ably uniform, flat plates. He thinks that the discovery of the anal tube in 

 Encrinus shows an interesting relation to the Fistulata, and that Encrinus 

 differs in the structure of the tegmen markedly from Ilolocrinus, Dadocrinus^ 

 Extracrinus, and Apiocrimis, and all older Artie ulata whose tegmens are 

 known; that it should not be united w^ith the Fistulata; but that it is a 

 highly specialized forerunner of the Articulata. 



The Austins ^ give a figure of Pentacriims hriareus (= P. fossilis) from 

 the Lias at Lyme Regis, showing a large tegmen composed of small, irregu- 

 lar plates. It rises in the middle into a conical protuberance, which looks as 

 if it might be the anal tube. No indication of ambulacra is given in the 

 figure. This is the same specimen figured by Buckland in the Bridgew^ater 

 Treatise, Geology and Mineralogy, Vol. IL, PI. 51, Fig. 2. Dr. Jaekel t 

 has described another specimen of the same species from the same locality, 

 which differs from the Buckland specimen and all others hitherto found, in 

 having the tegmen flattened so as to be fully visible from above, instead of 

 being laterally compressed into a conical protuberance. Neither mouth nor 

 ambulacral furrows are shown, though Jaekel says that the place where the 

 mouth must have been is indicated by the position and displacement of the 

 plates pretty near the middle of the perisome. Li the size and number of 

 plates composing the tegmen he thinks it somewhat resembles the structure 

 of the recent Pentacrinus naresianus. He expresses the opinion that in this 

 and in all other fossil tegmens the small plates close upon each other so 

 tightly and so irregularly that the course of the ambulacral furrows cannot 

 be fixed, and he thinks it probable that the tegmen will never be found 

 fossil in any other condition, as otherwise the soft disk could not survive the 

 process of decomposition, the motion of the w^ater, and the detaching out 

 of the matrix. This opinion of Jaekel emphasizes the extraordinary good 

 fortune by which these delicate structures are preserved in the specimens 

 described herein. Jaekel finds in his specimen '' at the place where from 

 analogy of the living forms one should expect to find the anus, a low pyra- 

 mid somewhat sunken upon itself, composed of low, broad plates, which 

 bear lateral projections, and on the outer side tubercles. They resemble 

 throughout the upper plates of the proboscis of Poteriocrinus multiplex. But 



* Monog. Rec. and Foss. Crinoidea, PI. XII., Fig. 16. 



t Sitzungsberichte der Ges. Naturf. Ereunde zu Berlin. Jahrg. 1891, Nr. 1, p. 7. 



