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gular ridges to the iutercostals, and by their lateral surfaces to each other. 

 They are obliquely truncated at their superior surfaces, excavated, and have a 

 horse-shoe-like impression, with a subperforated elevated transverse ridge. 



One of the hexagonal intercostal joints having one of the angular sides of its 

 superior surface elongated, has in a specimen in my possession (fig. 1.) a small 

 pentagonal interscapulary plate adhering, whose lateral edges connect with 

 the lower edges of the scapulae, and on whose superior surface another hex- 

 agonal interscapulary plate rests. To avoid an increased distance between the 

 the arms proceeding from the scapulae nearest to this interposed plate, they 

 themselves are smaller, and of a contracted form (fig. 5.) I cannot account for 

 this apparent irregularity in P. Crassus, but a similar one exists in the next 

 species, and in the genera in the division INARTICULATA. 



The intercostals and scapulae where they articulate to each other, must have 

 been very muscular, hence a contraction may be traced which produces a 

 waved appearance. 



I have not been fortunate enough to obtain a specimen extending beyond the 

 scapulae, but from the occurrence on the same slab, (see plate Poteriocrinites 

 Tenuis, fig. 10. and 1 1.) of joints of the arms, hands and fingers, which, in their 

 organic construction, resemble those of the Pentacrinites, 1 do not hesitate to 

 consider these as belonging to this species. I also have found small plates be- 

 longing to the integument extending over the cup-like abdominal cavity, and I 

 do not doubt its resemblance to that noticed in the Pentacrinites. 



In one instance I have observed a proof of the softness or muscularity of 

 the inside of the pelvis, one of its plates having retained the impression of a 

 columnar joint, which, by accident, came in contact with it previous to its 

 petrifaction. 



