new Species of Crinoids. 173 



species was provided with spines, and appears to be the small 

 variety of P. dumostim, Conrad*, which is of frequent occur- 

 rence in the same beds as this crinoid. 



In conclusion, I desire to express my grateful sense of the 

 kind assistance which Dr. P. Herbert Carpenter most willingly 

 afforded me in tracing out the relations of this crinoid, and 

 my thanks are also due to Dr. Henry Woodward, F.B-.S., for 

 permitting me to examine the fossil crinoids in the British 

 Natural-History Museum. 



Distribution. Middle Devonian, Hamilton group, Arkona, 

 Ontario, Canada. 



EXPLANATION OF PLATE VI. 



Fig. 1. Hystricrinus Carpenteri. A slightly compressed specimen, show- 

 ing the anal plate (A) with the anal interhrachial plates ahove 

 it (Ib.A). Attached to the vault of the crinoid is a specimen 

 of Platyceras erectum, Hall. Natural size. 



Fig. 2. The base (imperfect at the margin) of a small individual, viewed 

 from the exterior, showing the facet by which it connects with 

 the top of the stem, and the central canal. Natural size. 



Fig. 3. A detached first radial, with the second and axillary radials and 

 the lower joints of the arms. Natural size. 



Fig. 4. The sutural surface of the distal margin of part of a first 

 radial, showing longitudinal grooves and ridges where it con- 

 nects with the interhrachial plates, and radiating grooves where 

 it unites with the second radial. Enlarged three times. 



Fig. 5. The sutural surface of the lateral mariiin of two of the first 

 radials, showing oblique ridges and grooves. Enlarged three 

 times. 



Fig. 6. An imperfect specimen, with its surface partially covered with 

 spines. Natural size. 



Fig. 7. A portion of the surface of the same specimen, enlarged three 

 times, showing the spines, now prostrate, and the perforated 

 tubercles to which they were articulated. 



Fig. 8. A spine of the calyx, enlarged twelve times, showing interrupted 

 striae and microspines. 



Fig. 9. A spine of one of the vault-plates, similarly enlarged. 



Fig. 10. An imperfect individual, showing the smaller plates of the peri- 

 pheral portion of the vault and some of the interhrachial plates. 

 Enlarged twice. 



Fig. 11. A single plate, with wrinkled ridges and grooves, from the cen- 

 tral portion of the vault. Enlarged five times. 



Fig. 12. Plates from the central portion of the vault, covered with short 

 blunted tubercles and spines, similarly enlarged. 



Fig. 13. A fragment of the stem, enlarged twice, with two whorls of 

 mature cirri and an intermediate whorl of smaller cirri. 



Fig. 14. Another fragment of the stem, enlarged three times, showing 

 the socket of an anterior cirrus. 



Fig. 15. A facet of a stem-joint, enlarged four times. 



Fig. 16. A facet of a cirrus-joint, similarly enlarged. 



* Third Annual Report, New York Survey, Pal. Dept. 1840, p. 205. 

 Ann. & Mag. N. Hist. Ser. 5, Vol. xv. 13 



