6 Field Museum of Natural History — Geology, Vol. IV. 



No entire specimens of this species were collected by the writer, 

 but six fragments, Cat. No. P 10345, of sufficient size for identification 

 were found on the Patterson farm near Pontotoc, Mississippi. 



Cassidulus intermedius sp. nov. Plate I, Figs. 1-6. 



' Test oval, greatest width posterior to the center; rounded anter- 

 iorly, slightly rostrated posteriorly; dorsal surface convex, apex 

 eccentric anteriorly and inflated, sides declining about equally towards 

 the margins which are slightly inflated; the peristomal concavity 

 occupying more than half of the ventral surface. Ambulacral areas 

 narrow and flush, poriferous zones subpetaloid on the upper part of 

 the dorsal surface to a point varying in the different areas from about 

 one third to nearly one half the distance from the margin to the apical 

 system ; the zones are then contracted and continue as narrow bands 

 over the margin to the vicinity of the peristome, where they abruptly 

 widen, and again narrow to the peristome forming a floscelle. The 

 pores are distant and paired on the petaloid portion and in the flos- 

 celle; on the narrow connecting portions they are single, small and 

 indistinct. In the petaloid areas the pores of the outer rows are slit- 

 like, those of the inner rows round and smaller ; each pair is connected 

 by a groove. Interambulacral areas composed of large plates, the 

 plates nearest the peristome in each area inflated forming the bour- 

 relets. Dorsal surface covered with small crowded tubercles with 

 slightly sunken areoles, the tubercles on the ventral surface rapidly 

 increasing in size and distance apart as they approach the peristome. 

 A wide, longitudinal median band extends from near the anterior 

 margin through the floscelle to the posterior margin. This band is 

 without tubercles and the surface is smooth except where it passes 

 through the floscelle. The apical system in the type specimen is too 

 incomplete for detailed description, but appears similar to other species 

 of this genus. The peristome is situated slightly in front of the center 

 of the ventral surface, pentagonal, surrounded by a well-marked 

 floscelle, the bourrelets large and prominent, the phyllodes very 

 narrow as they reach the peristome and situated in grooves. The 

 periproct is elongated longitudinally and situated on the dorsal sur- 

 face at about one third the distance from the posterior margin to the 

 apex in a deep groove. The dimensions of the type specimen are: 

 Length 25.6 mm., width 22.7 mm., height 9.6 mm. 



This description is based on a single specimen, Cat. No. P 10346, 

 collected by the writer. The specimen had been slightly crushed on 

 the left side, a few of the plates of the left interambulacral area and 

 part of the apical system are missing, but the general form and all 



