14 



The vault is only moderately convex, covered with polygonal 

 plates and bears a subcentral proboscis. 



This species would seem to be more nearly related to Aciino 

 crinus nmltiraduitun, than to any other described species, but it 

 is so different in form and in surface ornamentation that no com- 

 parison is necessary to distinguish them. 



Found in the Burlington Group, at Burlington, Iowa, and now 

 in the collection of Wm. F. E. Gurley. 



PHYSETOCEINUS SAMrSONI, U. Sp. 



Plate I, fig. 5, nzygous side; fig. 6, opposite view; fig. 7, summit. 



Species medium size. Calyx obconical, rather broadly truncated 

 below and stelliform, as seen from above, in consequence of the 

 horizontal, rigid extension of the five radial series. The abrupt, 

 horizontal extension of the radial series commences at the top of 

 the third primary radials. Plates thick aud nodose. 



Basal plates form an hexagonal disc four times as wide as high, 

 stand upright and evenly truncated below. The first primary 

 radials are the largest plates in the body, about as long as wide, 

 three hexagonal, two heptagonal. Second primary radials about 

 one-third as large as the first and hexagonal. Third primary 

 radials about half as large as the second, pentagonal, axillary, and 

 support, on each superior side, a single secondary radial, which is 

 axillary, and supports, on each upper side, a single tertiary radial, 

 which gives to each ray four arms. There are, therefore, twenty 

 arms in this species. 



The interradial areas all connect with the vault, but they diU'er 

 much from each other. The first plate is about the size of a 

 second primary radial, and it is followed by two smaller plates, in 

 the second range. In one of the areas there are four plates, in 

 the third range, that separate the radial series and curve over 

 upon the vault, where they unite with the summit plates. In 

 each of the two areas, there are three plates, in the third range, 

 that unite with the plates of the vault. In the other area there 

 are two plates, in the third range, that are followed by three 

 plates, in the fourth range, that curve over and unite with the 

 plates of the vault. In the azygous area, the first plate is in line 

 with the first primary radials and like them, except somewhat 

 smaller. It is followed by two plates, in the second range, and 



