n^ .. ,. „ BEYOZOA. 221 



Montlculipora (?) oannonensia.] , 



been lateral (see transverse section, pi. XX, fig. 3) is now narrower and produced so 

 that it extends nearly across the center.of the zocecial cavity. This is shown best 

 in tangential sections, parts of two of which are represented in figs. 4 and 6 on plate 

 XX. Figure 4 shows the structure immediately beneath the surface, with small 

 acanthopores and numerous smaller pores in the walls and cystiphragms. In figure 

 6, showing the appearance at a slightly lower level, the walls are thinner and the 

 acanthopores apparently "wanting. Figs. 13 and 14 (plate XX) represent tangential 

 and vertical sections of a Kentucky specimen of this species in which we note an 

 unusual condition, namely, in some parts of the axial region there is a total absence 

 of both diaphragms and cystiphragms. In other parts of the same section, however, 

 these structures are developed in the usual manner, so that it is allowable to assume 

 that their occasional absence is merely an abnormal condition. The tangential 

 section represents a condition very nearly intermediate between figs. 4 and 6 of the 

 same plate. 



In many respects this species resembles Atadoporella ramosa, occurring in the 

 bed of shales next beneath, but the surface of the latter is more abundantly spinulose. 

 Thin sections, especially tangential, are easily distinguished. The true position of 

 the species seems to be nearer the froridescent variety of M. mammulata d'Orbigny, 

 described by Nicholson from the Cincinnati rocks under the name of M. molesta. 



Formation and locality.— Gale.na, shales at several points near Gannon Falls, Minnesota, and at 

 Decorah, Iowa. In Kentucky the species occurs in the Trenton shales between Burgin and Danville, 

 and at Frankfort. 



Mus. Reg. Nos. 7631, 8035. 8048, 8062. 



MONTICULIPORA (?) CANN0NENSI8, fl. Sp. 

 PLATE XX, FIGS. 10-12. 



Zoarium ramose, branches subcylindrical, 6 to 9 mm. in diameter, surface even, 

 without monticules, but exhibiting the usual clusters of large cells. These, however, 

 are inconspicuous in this species. Zooecia angular, with thin walls, about twelve in 

 3 mm. Mesopores and acanthopores apparently wanting, the occasional small cells 

 wedged between the ordinary zooecia being merely young or abortive. 



Internal characters: All that is known of these is shown in figures 10 to 12 on 

 plate XX. The characteristic features are (1) the greatly crowded diaphragms and 

 cystiphragms, (2) the presence of the latter throughout the length of the tubes, (3) 

 the unusual tenuity of, the walls in tangential sections, and (4) the almost total 

 absence and exceedingly small size of the acanthopores. 



The generic position of this species is somewhat in doubt. The ramose habit of 

 growth, and all the other characters save one, are indicative of Homotrypa. This 



