24 



imal side two tertiary radials, which gives to each of these 

 rays three arms. There are, therefore, in this species twelve 

 arms. The last tertiary and secondary radial, in each series, 

 is highly convex and the convexity extends below that of the 

 secondary radial and third primary radial below it, which 

 leaves a circular depression between the first primary radials 

 and the last secondary and tertiary radials. The margin of 

 the calyx thus seems to hang down and the ambulacral open- 

 ings are exposed, in a basal view, while they cannot be seen 

 in a summit view. 



There are three plates in each regular interradial area, the 

 first one rests between the superior sloping sides of the first 

 primary radials and extends up between the first secondary 

 radials. It is followed by two narrow elongated plates that 

 connect with two plates belonging to the vault. The first azy- 

 gous plate is in line with the first primary radials, nearly as 

 large and heptagonal. It is followed by three plates in the 

 second range, the middle one being the larger and extending 

 to a plate belonging to the vault. On each side of the su- 

 perior end of this middle plate there is an elongated narrow 

 plate abutting the first tertiary radial and extending to the 

 plates of the vault. There are, therefore, six plates in the 

 azygous area belonging to the calyx. 



The vault is only moderately convex, and is covered with 

 large, polygonal, tumid plates that hang over the margin so 

 as to hide the ambulacral openings from a summit view. At 

 the margin of the azygous area there is an elliptical, bulbous 

 prominence that shows no indication of having an orifice, from 

 an azygous side view; but on the top of it there is a small 

 opening partly surrounded by small plates. The orifice is ir- 

 regular aud an examination of it leads to the inference that it 

 was covered by small plates. Indeed, there can be little 

 doubt about it; and, if the orifice was not closed, by small 

 plates, it was minute and not the kind one would expect to 

 find in such a robust species. 



This is a strongly marked species, so different, in all 

 aspects, from those hitherto described, that no comparison will 

 aid in distinguishing it. 



Found by C. S. Hodgson, in whose honor we have proposed 

 the specific name, in the Burlington Group, in Adams county, 

 Illinois, and now in the collection of S. A. Miller, 



