BRYOZOA. 3038 
Monotrypa.] 
Diaphragms are few in the zoccial tubes, but in the mesopores, which are usually 
constricted at the point of crossing, they are abundant. Here and there the zoecial 
walls seem to diverge periodically so as to produce minute beaded tubuli. 
There is no parasitic bryozoan known to me from Lower Silurian rocks with 
which this species could be confounded. Ramose Bryozoa coated with it might be 
mistaken for certain varieties of Batostoma fertile, but the crusts are rarely complete 
enough to render such a difficulty common. A greater superficial resemblance even 
is sometimes presented to young examples of Pachydicta foliata, a truly bifoliate 
species, with very different internal structure and really so distinct that no one 
ought ever to confuse them. 
Formation and locality—Not uncommon ip the lower and middle thirds of the Trenton shales at 
Minneapolis and St. Paul, Minnesota. Occurs also in the ‘‘ Lower Blue” at Beloit, Wisconsin. 
Genus MONOTRYPA, Nicholson. 
Monotrypa (part.), NICHOLSON, 1879, Pal. Tab. Cor., p. 293; 1881, Genus Monticulipora, pp. 102 and 
168; ULRIcH, 1882, Jour. Cin. Soc. Nat. Hist., vol. v, p. 153; Foor, 
1883, Contri. Micro-Pal. Can., p. 14. 
Monotrypa, ULRicu, 1890. Geol. Surv. Ill., vol. viii, p. 379. 
Ptychonema, HALL, 1887, Pal. N. Y., vol. vi, p. xiii. 
Zoaria irregularly massive, discoid, or subglobose, apparently not divisible into 
mature and immature regions. Zocecia comparatively large, prismatic, with very 
thin, straight or transversely wrinkled walls; diaphragms complete, remotely placed 
in the tubes. Both mesopores and acanthopores wanting. 
Type: M. wndulata Nicholson, 
We are satisfied that the position of this genus is near Diplotrypa (sensu stricto) 
and the simple section of the genus Batostoma. In the last we have only the ramose 
habit of growth, and few and small mesopores and acanthopores to distinguish it 
from Monotrypa, the structure of the walls and the character of all the other points 
being precisely the same in the two groups. In Diplotrypa diaphragms are perhaps 
always more abundant, but in all other respects, excepting that the tapering prox- 
imal ends of the zocecial tubes are closely tabulated like mesopores, the structure is 
essentially the same as in Monotrypa. There is a largeness and a certain looseness 
of arrangement that distinguishes the whole family Diplotrypide from the Amplexo- 
poride, a family including (under Leptotrypa) a number of simple species agreeing 
otherwise closely with Monotrypa. These species of Leptotrypa (e. g. L. filiosa d’Orb. 
sp., and L. petasiformis Nich. sp.) belong, | am convinced, to a different line of devel- 
opment than that of true Monotrypa. 
