484 BULLETIN 106, UNITED STATES NATIONAL MUSEUM. 



PORELLA IRREGULARIS, new species. 



ri.-ite 02. fiiis. 18-21. 



De*c/'!/>f!/>n. The zoariuni inerusts shells and bryozoa. The zooecia are dis- 

 tinct, elongated and of irregular form, separated by a furrow; the frontal is convex 

 and formed of a tremocyst with numerous irregular pores. The a pert lira is visible 

 at the base of the peristomie: the peristome is thin, oval, salient. The ovicell is 

 globular, somewhat salient, little imbedded in the distal zooecia ; it is hyperstomial 

 and opens into the peristomie above the apertura; it is formed of a large area very 

 finely porous, surrounded by a small, very little salient collar. The oral avicu- 

 larium is median, placed in the sinus of the peristome, little salient, smooth. 



\hpe= 0.06-0.08 mm. . (3=0.55-0.65 mm. 



Measurements. Penstomice ,.' Zooecia , nnr An . 



1/^=0.12 mm. |Zs=0.35-0.2.> mm. 



Variations. The zooecia are quite rnrialili' in their form and in their micro- 

 metric dimensions even in the zoarial regions distant from the ancestrula (figs. 

 19, 20). In the interior (fig. 21) the small lyrula is visible. Figure 18 shows 

 numerous traces of incompletely developed ovicells; there are some semicircular 

 olocystal traces on the distal zooecia. The formation of the ovicell is therefore 

 much posterior to that of the zooecia : it probably ought to coincide with the maturity 

 of the ovary, as Jolliet thought in 1STT. 1 But what is the origin of the endocystal 

 bud which secretes the ovicellarian olocyst ? 



Affinities. This species differs from Poi'clla granul^osa in its polygonal tremo- 

 pores and its irregular zooecia. 



It differs from Porella coronata in the absence of all adventitious avicularia. 



Occurrence. Lower Jacksonian (Moody s marl) : Jackson, Mississippi (com- 

 mon). 



Cotypcs.Cat. Xo. 64145, U.S.KM. 



PORELLA GRANULOSA, new species. 



Plate 02. fig. 13. 



Description. The zoarium inerusts bryozoa. The zooecia are distinct elon- 

 gated, elliptical ; the frontal is convex, grunulose, and formed by a tremocyst with 

 numerous pores, separated by prominent granulations. The apertura is semilunnr 

 and scarcely visible exteriorly; the peristome is thin, somewhat salient, semilunar, 

 deformed below by the avicularium. The ovicell is globular, little salient, some- 

 what imbedded in the distal zooecia : it is formed of a large area, very finely porous, 

 surrounded by a smooth or granulose collar; it is hyperstomial and opens into the 

 peristomie above the apertura. The avicularium is very little salient; it deform- 

 the peristome and opens into the peristomie. 



rfi/>c'=0.07mm. . [7,2=0.45 mm. 



Measurements. 1 enstomice , Zooecia , 



[Ipe=0.l2 mm. 1/3=0.30 mm. 



1 Jolliet. Contributions :i 1' Uistovie nnturelle lies o>t>-s de t'nuiiT. Arc-hives de Zoologie experiment;!! i>t 

 ucniTiili', l':iris. 1ST", p. 75. 



