Revision of Bryozoan Genera.—Cumings. 21 
un 
undescribed form (probably the phase of D, subpulchella fig- 
ured on pl. IX of this paper). 
Another most interesting feature of the evolution of De- 
kayia, already hinted at, is the change from ramose to frondes- 
cent forms in passing from the Utica to the Lorraine beds. 
This tendency affects not only Dekayia but also Homotrypa,* 
and to a limited extent even the persistently ramose Callopora. 
In the Utica beds, shale predominates; while in the Lor- 
raine, limestone predominates ; and the conditions in the latter 
-were correspondingly more favorable to the growtn of Bryo- 
zoa (Trepostomata). We accordingly find in the Lorraine an 
immense number of species and individuals. In the succeed- 
ing shales (Dalmanella meeki zone)+ only a few Tre- 
postomata are met with, and these are ramose (Callopora, 
Bythopora, and a Dekayia quite similar to D. ulricht) ; but in 
the succeeding calcareous beds of the Rhynchotrema zone (up- 
per Richmond) # flat forms again abound. (Dekayia prolifica, 
D. Singularis, and several undescribed species of Homotrypa). 
I believe that the production of frondescent forms is mainly 
due to more luxuriant growth, and that this may affect any 
species. Any number of zocecia can be stowed on a flat zoa- 
rium without the necessity of unduly elongating the mature 
and submature regions. Again there is much less loss of space 
in the crowding together of flat than of round zoaria, as a mo- 
ment’s reflection will show. Luxuriant growth would also pro- 
duce coalescence of branches and exaggerated growth at the 
points of bifurcation, with corresponding flattening. 
Yale University, January, 1902. 
DESCRIPTION OF PLATE IX. 
Tangential Sections. 
Fig. 1. Dekayia ulrichi (Nich.), Ramose form, from the Utica beds 
at Cincinnati, O. 4 20. 
Fig. 2. Dekayia ulrichi-lobata n. var. Frondescent form, from the 
lower Lorraine, Manchester Station, Ind. + 20. 
* There is a truly ramose Homotrypa in the upper Utica, which in every- 
thing but the shape of the zoarium is a genuine Homotrypa curvata. 
+ The Dalmanella mecki fauna represents a recurrence of the Da/manelia 
multisecta fauna with practically the same physical conditions. This zone is 
not exposed at Richmond. 
t Middle Richmond of Nickles. His Upper Richmond is the same as the 
Madison beds of Foerste (Indiana, Dept. Geol. and Nat. Res., 21st Ann. Rep., 
p.218) Only the upper part of the Rhynchotrema zone is shown at Rich- 
mond, It is unfortunate that Madison, Indiana, cannot give itsname to the so- 
or pe Richmond formation. The whole formation is superbly exposed at 
Madison. 
