38 BRYOZOAN FAUNA OF THE ROCHESTER SHALE. 
NlCHOLSONELLA FLORIDA (Hall). 
PL XIV, figs. 10, 11; PL XXIV, figs. 1, 2. 
Callopora florida nail, Nat. Hist. New York, Pal. II, 1852, p. 14t>, pi. 40, figs. 2a-f. 
Lcioclemafloridum Ulrich, Geol. Survey Illinois, VIII, 1890, pp. 410, 4l>5. 
Liochma florida Grabau, Bull. New York State Mus., No. 45, 1901, p. 165, fig. 02. 
Lioclema (? Nicholsonella) floridum Niekles and Bassler, Bull. U. S. Geol. Survey No. 173, 1900, p. 304. 
Zoarium an explanate expansion varying from 3 to 10 mm. in thickness and sometimes 
attaining a width of 50 mm., although the specimens aie usually seldom over 25 mm. wide. 
Base marked with a wrinkled epitheca. Celluliferous surfaces without monticules, even, 
the macula? being inconspicuous and composed of groups of zooecia of the normal size hut 
separated by interspaces slightly wider than usual. Zooecia large, rounded, two to three in 2 
mm., and on an average slightly less than 0.5 mm. in diameter. Apertures floriform, the 
acanthopores inflecting the zooecial walls which encroach upon the zocecial cavity. Inter- 
zooecial spaces open in young specimens and showing one or two rows of mesoporcs separat- 
ing adjoining zooecia, but in old specimens closed with a solid, granulose deposit. Acan- 
thopores large, numerous, averaging four or live to each zooecium, and inflecting the walls 
so as to give the floriform or petaloid appearance to I he zooecia! aperture. 
Internal characters. — Carefully prepared vertical sen ions show a very short, immature 
region in which the zooecia are prostrate, and all hough their walls are of a clearer structure 
than that obtaining in the mature zone, even here ftieir indistinct nature is clearly shown. 
With the inception of the mature region, the Lend to which is quite abrupt, mesopores and 
acanthopores are developed. Here the wall structure already noted becomes slill less dis- 
tinct, and, finally, in the older parts of the zoarium, the walls of the zooecia; and especialhj 
of the mesopores, become obliterated by a deposit of granular tissue. Diaphragms are 
inserted in the zooecial tubes at an average distance apart of a trifle less than their own 
diameter. The diaphragms of the mesopores are at a like distance from each other, hut 
because of their narrower diameter appear more crowded. 
As is usual in most Trepostomata, the diaphragms are more abundant in the later than in 
the earlier parts of the mature region. The acanthopores of this and of the following 
species are quite different from the normal form of this structure, as they are seen in \ eri ical 
sections to be simply tubes with a more or less definite wall inclosing a central clear space. 
No trace of the usual laminated tissue arranged in cone-like layers and pierced vertically by 
a central canal can be observed. 
Tangential sections present various appearances, according to the portion of the zoarium 
cut by them. At the beginning of the peripheral regions the walls of the zooecia and meso- 
pores art 1 thin and although hazy in structure are still fairly clear. Here the acanthopores 
are small and inconspicuous. Higher up in the mature region the walls are considerable 
thickened and the acanthopores have increased in size and number. Finally, in flu" most 
mature or aged condition, the interzooecial space is occupied by a granular tissue obscuring 
the mesopores and through which the acanthopores pierce. 
The large, rounded, isolated zooecia, floriform apertures, closed interspaces, numerous 
acanthopores, and explanate growth, are characters which make the identification of this 
species quite easy. The closely related form N. ringuebergi n. sp. is distinguished by the 
presence of much smaller zooecia. TAOclema explanatum has a similar method of growth hut 
the smaller zooecia and open mesopores are points of difference distinguished by the unaided 
eye. Internally the two are also quite different as their respective generic references 
indicate. 
Occurrence. — Not uncommon in the Rochester shale at Lockport, Rochester, Niagara 
Falls, and Lewiston, N. Y.; Grimsby and Thorold, Ontario; Osgood beds, Osgood. Ind. 
Specimens that can not be distinguished from the typical New York form occur m the 
Silurian strata of the island of Gotland. 
Catalogue numbers, 35510, 35511, U S. National Museum. 
