LOWER HELDERBERG ROCKS. 
in 
There are sometimes variations in the arrangement of the brachial plates, in which 
the intercalated or central range of plates above the first bifurcation consists of one 
plate below, succeeded by two ranges of two each, and two in single series above; 
and sometimes of a single range of three plates, one above the other. It is probable, 
however, that the number and arrangement of these small plates are not constant. 
The arms of this species of Mariacrinus are so nearly like those of the associated 
species of Platycrinus , that in detached fragments they may readily be mistaken for 
the same. 
Fig. 6. A small individual preserving the body and arms nearly entire, with a small portion 
of the column. 
Fig. 7. A larger individual. 
Fig. 8. Enlargement of the body of fig. 6. 
Fig. 9. Enlargement of the arm-joints and tentacula. 
Fig. 10. Enlargement of the rays and base of the arm-joints. 
Fig. 11. Diagram showing the structure of the body and arrangement of the brachial plates. 
Geological position and locality. In the shaly layers of the Pentamerus limestone, 
associated with the preceding species : Wheelock’s hill, Litchfield, Herkimer county. 
Mariacrinus issacropetalus (n. s.). 
Plate III A. Fig. 1 & 10, 11, 12 ; also Plate III B. Fig. 1 & 2. 
Body large, hemispheric. Basal plates very wide and short. First radial 
plates much wider than high, four heptagonal and one hexagonal. 
Second radial plates pentagonal (?) : third radial, pentagonal; all 
wider than high. Brachial plates large ; lower ones hexagonal; second 
series pentagonal. Interradial plates one, large, nine- or ten-sided, 
succeeded by two smaller pentagonal plates. 
Arms unknown. 
Column large, round, deeply inserted into the base of the body. 
The specimen described consists of the base and a portion of two series of the 
radial plates, and one series of interradial plates. The general structure, as far as 
visible, is so much like other species of this genus, that I have little hesitation in 
referring it to the same. The diameter of the base and size of the plates are about 
twice as great as in M. nobilissimus; and the entire body and arms, of the same 
general character as in that species, could scarcely have been less than nine or ten 
inches. 
