PALEONTOLOGY OF IOWA. 485 



spending in number and in their bilateral arrangement with 

 those of the lateral pores, complete the series of poral pieces. 



" A central pentagonal opening is seen on the summit : this corresponds to the 

 mouth of the animal. It is surrounded by four other smaller openings in the summit 

 of the interradial pieces, and divided in the middle by a longitudinal lamella : the 

 opening in the fifth radial piece, a little larger than the four others, has two lamellae, 

 which form three canals, of which the middle one corresponds to the anus, and the 

 two lateral ones, as those of the other radial pieces, to oviducts of the animal. 



" The stem is formed of little cylindrical articulations, having a very small circu- 

 lar opening : it appears to have been very short." 



Peiitremites subtrancatus (n.s.). 



PLATE II. FIG. 3. 



TURBINATE or reversed pyramidal, the base round, gradu- 

 ally becoming angular above, distinctly pentangular at the 

 base of the pseudambulacral spaces ; base small, almost 

 pointed, apex broad subtruncate above ; basal plates small, 

 less than half the length of the body ; radial plates less than 

 once and a half as long as the basal plates, slightly divided 

 above for the reception of the pseudambulacral plates ; in- 

 terradial plates small, rising above the centre when complete ; 

 summit convex, flattened in the centre ; pseudambulacral 

 spaces short, abruptly convex in the middle ; poral plates 

 fifteen or more in each series ; ovarian apertures small, 

 round. 



This species belongs to the same type of form as P. reinwardti, from which the 

 one here described differs in having relatively a much shorter base, is more rapidly 

 expanding above, the summit less elongated and much more obtuse, there being little 

 contraction from the pseudambulacral spaces to the summit of the interradial plates. 

 The pseudambulacral spaces in P. reinwardti are much narrower and the sides more 

 nearly parallel; the poral plates present a flattened or depressed line, while in this 

 one they form an abrupt convex area. 



A similar species P. striatus, from the Corniferous limestone, has the plates deeply 

 striated parallel to their margins, and the pseudambulacral areas broader and less 

 abruptly convex, and the interradial plates less extended. 



Geological formation and locality. In the calcareous shale of the age of 

 the Hamilton group of New-York : New-Buffalo, Iowa. 



