BRYOZOA. = 251 
Prasopora insularis.] 
but the principal peculiarity is found in the cystiphragms, these appearing as series 
of semicircular lines, each distinct from the other, on one or both sides of the zocecial 
tubes. In the latter case they are arranged alternately. About three cystiphragms 
occur on each side in 1 mm., while in the same distance six or seven diaphragms 
cross the space left by them. This is the usual arrangement of the cystiphragms, 
but in many of the tubes they also form loose connecting series very much as in 
P. similatriz, var. orientalls (see plate XVI, fig. 2). 
This species is certainly distinct from P. simulatriz, the isolated condition of 
the cystiphragms being too striking a feature to be considered as less than specific. 
Foord’s P. affinis and P. oculata, the first especially, are closer relatives, having like- 
wise the cystiphragms isolated and not forming continuous series. ‘he first, a 
smaller species, with no macula, and conical instead of semicircular cystiphragms, 
is known as yet only from Canada.* P. oculata, however, has been found in Minne- 
sota, and is described on a succeeding page. 
Formation and locality.x—Dr. Nicholson’s types of the species are from the Trenton limestone of 
Peterboro’. Ontario. Foord says the species ‘tis very abundant throughout the Trenton formation of 
Canada.” Also that it has been found in the upper beds of the Chazy, at Nepean, near Ottawa. The 
Minnesota specimens were collected by the author in the upper part of the Galena shales near Cannon 
Falls. It is there associated with Monticulipora grandis Ulrich, another massive but more irregularly 
growing form, that was at first believed to be restricted to the top of the lower limestone. 
PRASOPORA INSULARIS, ”. Sp. 
PLATE XVI, FIGS, 18-23. 
Zoarium small, discoid, plano- or concavo-convex, commonly from 15 to 20 mm. 
in diameter;and 5 or 6 mm, in hight. In a very large example these dimensions are 
respectively 28 and 12 mm., while in the smallest seen they are 1.5 and 0.5 mm. 
Under surface with a central scar, and beyond it delicate radiating lines, fine con- 
centric striz, and, at intervals indicating stages of growth, stronger wrinkles. Very 
often the zoaria are evidently made up of distinct superimposed layers, but these are 
not usually distinguishable internally. Upper or convex surface without monticules, 
but exhibiting, at intervals of about 4 mm., distinct clusters of large zocecia. Gen- 
erally, at the center of each of these clusters, the mesopores which are small and in 
nearly all cases just about numorous enough to isolate the zowcia, are gathered into 
groups of varying size. Zocecial apertures circular, those in the clusters attaining a 
diameter of 0.4 mm., while those of the smaller size in the inter-macular spaces 
average about 0.22 mm., with eleven or twelve in 3 mm, 
*Since writing this a number of specimens of P. affinis were collected near Cannon Falls in the upper part of the 
Galena shales, associated with species of Nematopora and Arthroclema armatum. 
