610 GEOLOGICAL SURVEY OF IOWA. 



above the other plates. Second radials wider than long. 

 Third radials supporting, on the two upper oblique sides, 

 two hexagonal supraradial plates, and these each supporting 

 a pentagonal second supraradial : each of these supports two 

 brachial plates, from the upper sides of which proceed the 

 arms, giving uniformly four arms to each ray. A small 

 heptagonal intersupraradial plate rests on the adjacent edges 

 of the first stipraradials. 



First interradial plates heptagonal or octagonal; the an- 

 terior ones large, supporting two or three plates in the second 

 and third range each. First anal plate as large as the first 

 radials, strongly tuberculiform, supporting in the second 

 range three plates and in the third range four, with some 

 small plates intercalated between the arms. Dome large, 

 becoming proboscidiform. Surface granulose, the granules 

 sometimes pustuliform. 



COLUMN large, consisting of strong joints separated by 

 thinner ones, and, farther from the body, by two, three, four, 

 or more thinner ones. 



This species is peculiar in character. The body, composed of large strong plates, 

 is surmounted by the projecting bases of the arms, from which the latter rise ver- 

 tically, being inserted upon the top and within the margin of the brachial plates. 

 The proboscis is remarkably large and strong : it is somewhat crushed in the spe- 

 cimen fig. 4, pi. 15, the base only remaining; while in fig. 4, pi. 16, the lower part 

 is well preserved to the height of six or seven plates above the axils. 



PLATE xv, fig. 4. View of the postero-lateral side of a large specimen. 



PLATE xvi, fig. 4 a. Anterior side of a well-preserved specimen. [ The figure is too 

 broad below, and the brachial margin is not sufficiently pro- 

 minent.] 



" fig. 4 b. A similar view of another specimen, representing more perfect- 



ly the form of the base. 



The following diagram (fig. 92) illustrates the form and proportions of the plates of 

 this species, from the specimen fjg 4, pi. 15. There is some irregularity in one of the 

 interradial series, as shown in the figure, which has produced a slight distortion in 

 the anterior ray. There js a single intersupraradial plate which is truncated above, 

 and upon which rests a small plate with its upper extremity thickened and elevated 

 above the brachial plates. The articulating surface for the arm-plates scarcely occupies 

 more than onevthird the width of the brachial plates at their summits. 



In the smaller specimen figured on Plate xvi, fig. 4 a, there is a second narrow 

 plate between the brachial plates of each division of the ray, and the third series of 



