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 zorecial 

 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. similatrix, var. orientalls (see plate XVI, fig. 2). 



This species is certainly distinct from P. simulatrix, 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. The first, a 

 smaller species, with no maculae, 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. Dr. Nicholson's types of the species are from the Trenton limestone of 

 Peterboro'. Ontario. Foord says the species "is 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, n. sp. 



PLATE XVI, PIGS, 18-23. 



Zoariuni small, discoid, piano- 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 stria), 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 zooecia. Gen- 

 erally, at the center of each of these clusters, the mesopores which are small and in 

 nearly all cases just about numerous enough to isolate the zooecia, are gathered into 

 groups of varying size. Zooacial 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 writlug this a number of specimens of P. afflnus were collected near Cannon Falls In the upper part of the 

 Oalena shales, associated with species of Nematupora and Artliroctema armatum. 



