1889.] 
345 
[Foerste. 
to fifty-five in number, and on the exterior five ribs occur in a 
width of 5 mm. at 25 mm. above the base. The surface is also 
finely striated transversely. Longitudinal sections indicate that 
the calyces have a depth of at least 8 mm., the sides of the calyces 
descending rapidly. 
Diaphragms certainly occur in the regions below the calyx, but 
our sections did not reveal any dissepiments in the calyx. The 
rock in which they occur is almost a pure, white lime, and the 
structure was difficult to determine in our specimens. It was im- 
possible with the collections at hand to distinguish from this spe- 
cies certain forms often irregularly bent, or unusually elongated 
which show similar vertical ribs, although the transverse wrinkles 
and striae are usually more developed. 
Streptelasma calicula, var. geometricus, var. nov. 
(PLATE IX, FIGS. 7,13,12.) 
Of this form, the two smaller specimens figured belong to my 
own collection, the larger specimen to that of Mr. B. B. Thresher. 
The specimens are simple, usually slightly curved at the base, the 
greater convexity being on the side of the apertural gap. Above 
the base the polyp is perfectly erect and symmetrical. In some 
specimens the base itself is erect. The polyps taper regularly to 
the base, such constrictions as are found not exceeding in size the 
form of well-marked wrinkles and being of no structural value. 
The angle formed is usually about 45° or 50°. The surface of the 
specimen is ribbed longitudinally, the ribs corresponding to the 
number of septa within. Most of the specimens found do not ex- 
ceed 20 mm. in height. The number of ribs on the exterior of 
these varies from fifty-two to seventj^-two. 
There are usually five ribs in a width of from 3 to 3.3 mm. The 
ribs are moderately convex, very distinctly differentiated and are 
crossed by fine striae. A longitudinal section shows that the ca- 
lyx has abruptly descending walls and is 7 or 8 mm. deep. The 
diaphragms are arched between the centre of the polyp and its 
walls, descending at the centre and apparently forming an invagi- 
nated tube there, also crossed by diaphragms. We have not enough 
sections to determine the matter definitely ; the same is true as to 
the existence of dissepiments between the septa of the calyx, 
