28 
Remarks. This form is rather closely related to the typical L . mam- 
milare of the St. Louis of the Mississippi Valley region. There are appar- 
ently, however, some rather constant differences. The corallum of the 
latter appears to be shorter and broader. The corallites usually have a 
greater diameter and a deeper cup (about 7 mm. deep), and the columella 
does not extend so nearly to the surface. The dissepiments meet the walls 
more acutely, usually in both mature and immature specimens at an 
upward pointing angle of about 50 degrees. The dissepiment-free centre 
has a width similar to the Minnewanka form and like it, upon weathering, 
often stands free from the rest of the corallite. Upon examining the very 
large collection in the Museum of Comparative Zoology (through the 
courtesy of Professor Raymond) these criteria were found to usually hold, 
though some silicified specimens, labelled “Subcarboniferous of Bloom- 
ington, Indiana,” had cups shallow, with the tip of the columella reaching 
as high as the sides of the cup, and many tabulae meeting the walls at an 
angle of 90 degrees; these may represent merely accelerated individuals. 
In old corallites of L. mamillare, the outer part of the calyx tends to flatten 
out into the typical condition seen in the mature specimens of the L . 
pennsylvanicum, whereas the immature corallites of the latter are in this 
respect like the adults of the former. Typically in L. pennsylvanicum the 
middle half only of the calyx is conspicuously depressed, the outer part 
being almost flat. Another conspicuous difference between the two Bpecies 
is the presence in the bottom of the calyx of L. mamillare of a broad con- 
vexity from the centre of which rises the short columella; this convexity 
(the source of the name mamillare) is half the width of the corallite and 
rises prominently in the bottom of the calyx. It is practically absent in L. 
pennsylvanicum except in some of the younger corallites. 
L. pennsylvanicum appears to resemble most closely L. microstylum 
White 1 reported from the Chouteau limestone of Sedalia, Missouri, that is, 
in so far as can be judged from the very brief description and from the 
figure. Therte is, however, doubt as to the locality of the very poorly 
preserved type specimen, the only specimen known. White founded this 
species upon the “flatness or shallowness of the calyxes, the smallness of 
the central pit, and of the columella.” It resembles L. pennsylvanicum in 
the flatness of its calyxes, the practical absence of the inverted, funnel- 
shaped tabulae from the calyx, and in the small prominent columella. It 
has, however, a much narrower central pit, which in a corallite of 15 mm. 
diameter has a breadth of 3 mm., whereas a corallite of similar size in L. 
pennsylvanicum has a breadth of 9 mm. This conspicuous difference, 
together with its many unknown characters and its given horizon as Lower 
Mississippian, led to the rejection of L. microstylum for the Albertan form. 
A specimen at Harvard University, collected by Dr. W. P. Haynes from 
south of Virginia City, Montana, belongs to this species. 
Locality and Horizon . In the Pennsylvanian ? of southern Montana. 
In the Minnewanka region in the Pennsylvanian of sections 1-33 (c); 
2-6 (C); 8 (C), 14 (C); 3-10 (C); 3a-4 (C). 
1 {J.S. Geol. and Geog. Surv., 12th Ann. Bept.. PI. 40, fig. 7a, p. 159. 
