268 THE PALEONTOLOGY OF MINNESOTA. 
{(Heterotrpya prolifica. 
Hetrerotrypa prouirica Ulvich. 
(Not Figured.) 
Hetcrotrypa prolifica ULRion, 1890. Geol. Surv. Ill., vol. viii, p. 418, pl. xxxvii, fig. 1-1d. 
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 
10cm. 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. 
Zocecial 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 zoecial 
tubes. Acanthopores a little more than one-third as numerous as the zocecia ; when 
not situated at the angles, generally inflecting the zocecial cavity a little.” 
“This species approaches quite closely to H. frondosa d’Orb., having a somewhat 
similar growth ; but in that species the zocecia 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. 
Hetrerotrypa sinautaris Ulrich. 
(Not Figured.) 
Heterotrypa singularis ULRICH, 1890. Geol. Surv. ll, vol. viii, p. 415, pl. xxxvii, figs. 3-8e. 
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. Zocecia about nine in 2 mm., angular and thin-walled in the axial, 
subeircular 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 subcireular. Diaphragms developed very irregularly, at times but few 
