REPORT OF THE STATE PALEONTOLOGIST I903 275 



lower border of the anus; plates 22 and 23 form the right and a 

 portion of the upper border of the anus, and 23 also supports the 

 first and half the second brachial of the posterior arm. Plate 24 is 

 just anterior to and also supports the first brachial of this arm, it 

 also reaches the mouth and forms part of its border; plate 25 is 

 semicircular in outline, fills up the inner portion of the half sigma 

 of the anterior arm and supports all of its brachials on this side ; its 

 inner border is raised tO' form the edge of a channel which receives 

 the eight grooves of the anterior brachials. Plate 26 borders on the 

 mouth, supports the posterior edge of the first anterior brachial, and 

 bears the genital pore; 2J is formed like 25 and receives the six 

 grooves of the posterior arm ; 28 supports the last brachials of the 

 posterior arm on the outer side of the curve and with 29 forms the 

 left border of the anus. At the point where plates 26, 27 and 28 

 meet each other there is a peculiar, small, roughened mound which 

 may represent the madreporite. 



There is considerable variation in the plate arrangement in the 

 three specimens figured. vSpecimen C was probably as aberrant a 

 form as could have been found in the two hundred or more speci- 

 mens collected. This specimen has 37 plates besides the brachials, 

 A had 29, and B shows but 28.^ The four plates bordering the 

 mouth are constant and may be called the orals. They bear cover- 

 ing plates some of which may be seen in specimen B [pi. i, fig. 5]. 

 The plates I have called brachials are vertical plates with their lower 

 edges resting on the neck plates of the theca and their middle por- 

 tion against the opposite oral. These plates do not show covering 

 pieces but the orals numbered 25 and 27 still continue their cover- 

 ing pieces w^hich now reach completely across the food groove, form- 

 ing a single series of rectangular plates. There were several of these 

 in position on the anterior arm but they became lost through an 

 accident and the only completely transverse plates now present are 

 in the posterior arm. The first one or two brachials are the largest ; 

 the others then grow rapidly smaller as the half sigma recedes from 

 the mouth. All bear truncate faces on their distal ends and the 

 larger are marked as if they had borne extended and movable 

 brachioles. The larger faces are directed more nearly upward and 



^Compare figures i, 2 and 3 of the text. 



