268 THE PALEONTOLOGY OF MINNESOTA. 



[.Heterotrpya prolifica. 



HETEROTRYPA PKOLIFICA Ulrich. 



(Not Figured.) 

 Heterotrypa prolifica Umicn, 1890. Gcol. Surv. 111., vol. viii, p. 413, pi. xxxvii, flg. 1-ld. 



Original description: "Zoarium frondescent, or subramose with much flattened 

 branches ranging in thickness from 4 to 12 mm., and at times attaining a hight of 

 10 cm. Low rounded tuberosities arranged in irregularly intersecting lines, and 

 composed of cells a little larger than the average, commonly surrounding a cluster 

 of mesopores, serve to break up the monotony of an otherwise smooth surface. 

 Zoo3cial tubes curving in the axial region, direct throughout the peripheral region, 

 where their walls become considerably thickened. Zocecial apertures subpolygonal, 

 about eight in 2 mm., and 0.15 to 0.18 mm in diameter. Interspaces occupied by 

 calcareous matter ; where very wide by a few mesopores with illy-defined walls. 

 Most of the mesopores are found in the clusters. 



A few diaphragms in the axial region; in the transition period they become 

 more numerous; in the cortical region they are close set, a tube diameter or less 

 apart. In the outer portion of this region they are often concave, sometimes tend- 

 ing to the infundibular form. Mesopores more closely tabulated than the zooecial 

 tubes. Acanthopores a little more than one-third as numerous as the zocecia ; when 

 not situated at the angles, generally inflecting the zooecial cavity a little." 



" This species approaches quite closely to //. frondosa d'Orb., having a somewhat 

 similar growth ; but in that species the zooecia are more angular, the walls thinner, 

 mesopores far more numerous, and the acanthopores rather more abundant." 



Formation and locality. A common form in the upper beds of the Hudson river group at many 

 localities in Ohio and Indiana, also at Wilmington, Illinois, and Iron Ridge, Wisconsin. 



HETEROTRYPA SINGULARIS Ulrich. 



(Not Figured.) 

 Heterotrypa singularis ULKICII, 1890. Geol. Surv. 111., vol. viii, p. 415, pi. xxxvii, figs. 3-3e. 



Original description: "Zoarium subramose, at times attaining a thickness of 7 

 cm. Surface smooth or nearly so, with clusters of cell apertures a little larger than 







the average. Zoo3cia about nine in 2 mm., angular and thin-walled in the axial, 

 subcircular in the mature region. There are commonly two or more successions of 

 immature and mature regions. Mesopores of variable size, very numerous, usually 

 angular or subcircular. Diaphragms developed very irregularly, at times but few 



