210 THE PALEONTOLOGY OF MINNESOTA. 



[Phylloporlna reticuUta 



Obverse face of branches strongly convex, carrying three to five rows of zooecial 

 apertures. These are subcircular, with a scarcely appreciable peristome, 0.09 ram. 

 in diameter, and twenty-three to twenty-five in 5 mm. in each row. Interspaces 

 depressed, generally forming distinct pits between the ends of the cells. Sometimes 

 obscure raised lines may be detected between the rows of apertures. Acanthopores 

 small, usually abundant, with no definite arrangement. 



Thin sections show that the tubular primitive portion of the zooccia, which is 

 long and prismatic, is often intersected by from one to three diaphragms. Just 

 before bending outward to open at the surface the tubes become rounded, leaving 

 irregularly shaped interspaces or shallow mesopores. It is here also that the acan- 

 thopores are developed. 



^ 



In some respects this species occupies an intermediate position between P. tren- 

 tonensis Nicholson, sp., and P. granistriata Ulrich, both of which occur in higher beds 

 of the Trenton, proper. The first is more robust, with stronger branches, more 

 numerous rows of zooecia, and the primitive portion of the zocecia longer and 

 straighter. The zoeecial apertures are also more angular. The second has more 

 rigid branches, longer and narrower fenestrules, and the reverse side of the branches 

 grano-striate and on the whole more delicately marked. The fenestrules of P. reti- 

 culata Hall, sp., are so much smaller that even very small fragments may be dis- 

 tinguished at once. 



Formation and locality. The Tennessee type specimens are from the Glade limestone at Lebanon 

 and La Vergne. Fragments of probably the same species occur in the " Pierce limestone " atMurfreesboro. 

 The Minnesota examples were obtained from the lower part of the limestone at Minneapolis. 



Mus. Beg. No. 5954. 



PHTLLOPQRINA RETICULATA Hall. 



PLATE IV. FIGS. 8-15. 



Intncaria retieulata HALL, 1847. Pal. N. Y., vol. i, p. 17. 



Phylloporina retieulata ULKICH, 1890. 111. Geol. Surv., vol. viii, pi. LIII, flgs. 2, 2a. 



Specimens as seen, consisting of small, flat or undulating, reticulate expansions, 

 being in each case evidently fragments of a depressed, funnel-shaped zoarium, prob- 

 ably not exceeding 5 cm. in diameter. Branches rounded in section, 0.2 to 0.3 mm. 

 in diameter, inosculating at unusually frequent and regular intervals. Fenestrules 

 somewhat elongate, about as wide as the branches, subrhomboidal in shape in the 

 more regularly constructed fragments ; their number in a given space is fairly con- 

 stant, the extremes noticed in 1 cm. being ten and twelve. Reverse of branches con- 

 vex, finely striated lengthwise. 



