FROM THE PALEOZOIC ROCKS OF INDIANA, KENTUCKY AND OHIO. 



451 



The single second radial of the first series is very rough, marked by high, interrupted 

 ridges crossing it toward the centre of the adjoining pieces. 



The markings upon the first and second radials separate this from the preceding species. 

 Our specimen is of an individual a little less than H. discus. It differs from that species 

 in the pentangular pit, and the more robust character of the plates. 



The column appears to have been round, or subpentangular at its junction with the 

 body. 



Size of Specimen. 



INCHES. 



Greatest length of first radials, 62 



Least length of first radials, 47 



Height of first radials (vertical), 25 



Diameter of base, 3? 



Locality. — Same as last. 



Notice of some Peculiarities in the Structure of Crinoidal Columns, and the Attachment of 



the Column to the Body of the Animal. 



PI. XXVT, Fig. h. 



In a great variety of crinoidal columns, referred to many genera and species, the attach- 

 ment of the column is by a simple disk, having a plain or crcnulatcd surface at the points 

 of attachment to the body ; the disk, by which the column joins the body, being the 

 last joint of tin; body. Usually the disk is crenulated, varying in the character of the 

 markings with the genera or species to which it belongs ; sometimes the marks are only 

 on the margin of the disk ; in other species the striae covers the entire surface of the place 

 by which it attaches to the body; in some the lines are straight, in others wavy or zigzag. 



In columns found attached to the bodies of several species of Dolatocrinus, the whole 

 structure and arrangement of the superior extremity of the column differs from the forms 

 referred to in a remarkable manner. 



In one specimen, in which this variance from the usual form is clearly and distinctly 

 seen, the column is round from a point half an inch below the calyx. In the specimen, 

 the round disks composing this part of the column are about twelve in number, with 

 twelve thin muscular (?) pieces between them, — the number varying with the age of the 

 animal. The round disks, forming the plain part of the column near the calyx, decrease 

 in size, descending about one-half of the pieces, when they increase slightly for the lower 

 portion. On the superior plain disk of the column are placed about ten pieces (varying 

 in number), rapidly increasing in size as they ascend — alternately thick and thin pieces. 



