40 BULLETIN 16 5, UNITED STATES NATIONAL MUSEUM 



with two very small lateral indentations; the peristome is thick, 

 salient, and bears two distal hollow spines. The ovicell is a salient, 

 cylindrical, transverse pad, hyperstomial, placed on the distal 

 zooecium. 



Measurements. — 



A (Aa=0.07mm. „ . (Zs = 0.57 mm. 



Apertura , _ io Zooecia 1 7 n K A K . 



r [?fl=0.13mm. yz = 0.5-0.54 mm. 



„ . „ f hov = 0.21 mm. 

 Ovicell \ 7 n KA 



1 /ov — 0.54 mm. 



Variations. — The aliform expansions of the frontal are character- 

 istic but quite sporadic ; at Vincentown they are rare, although they 

 are more frequent at Blackwoodstown. They mark certainly the 

 place of the ovicell, but it is impossible to determine whether they 

 are young ovicells in process of formation or old broken ovicells. 



The two distal spines are rarely visible, but they appear on the 

 better-preserved specimens. Rarer still are the opesiules. They are 

 almost always closed by fossilization and appear only in the very 

 special conditions of preservation. 



The recognition of the exact structure of fossil species is often 

 difficult because of the alterations that they undergo under the more 

 diverse influences. Subsequent calcification by infiltration of super- 

 ficial waters is the great enemy of the paleontologist, for it pene- 

 trates all the small pores and forms secondary ornamentations, often 

 difficult to differentiate from the primitive structure. This is fre- 

 quently the case in Monoporella. 



Affinities. — Monoporella vincentawnensis differs from M. laticella, 

 new species, in the much smaller micrometric dimensions and in the 

 presence of lamellar frontal expansions. 



Occurrence. — Vincentown limesand: Rather rare at Vincentown 

 and near Blackwoodstown, N.J. 



Holotype and plesiotypes. — U.S.N.M. No. 52606. 



Genus RHAGASOSTOMA Koschinsky, 1885 



RHAGASOSTOMA AMERICANA, new species 



Plate 8, Figure 7 



Description. — The zoarium encrusts the debris of shells. The zooe- 

 cia are distinct, elongated, hexagonal ; the mural rim is thick, salient, 

 granular; the cryptocyst is deep, large, flat, smooth. The opesium 

 is semielliptical, terminal, transverse, with proximal border some- 

 what convex; the opesiular indentations are small, sublinear, very 

 short, divergent. The ovicell is hyperstomial, not closed by the 

 operculum, globular. The onychocellarium is primoserial, much 

 elongated, fusiform, with rounded beak; the opesium is elliptical, 



