BRYOZOA. 315 
Nicholsonella laminata.] 
There is very little likelihood of confusion between the present species and any 
other referred to the same genus, and thin sections will of course distinguish it at 
once from species of other genera. Among the latter Monticulopora arborea, from 
higher rocks, is strikingly like N. pulchra superficially. 
Formation and locality—Not uncommon in the ‘‘ Pierce limestone” at Murfreesboro, Tennessee, 
where it is associated with an abundance of fossils, chiefly Bryozoa. 
Mus. Reg. No. 8131. 
NICHOLSONELLA LAMINATA, 2. Sp. 
PLATE XXI, FIGS 15-19 and 21, 
Zoarium laminar, several mm. thick, the under side strongly wrinkled concen- 
trically. Upper surface even, but exhibiting rather indistinct macule or areas in 
which the interspaces between the zocecia are wider than usual. Zocecial apertures 
circular, regularly arranged, nine or ten in 8 mm., averaging 0.2 mm. in diameter 
and 0.13 mm. apart. Peristome thin, very minutely papillose. Interspaces occupied 
by angular mesopores forming a complete series between the zowcia. Mouths of 
mesopores closed or open. When closed the interspaces are slightly roughened by 
small granules among which a few of larger size (? acanthopores) have been 
detected. Internal characters as shown in figures. 
I have taken great pains to illustrate the internal characters just as they 
appeared to me under the camera lucida, and I refer the student to figs. 15, 16 and 
17, rather than attempt a description. I will however admit at once that I do not 
understand the purpose of the system of dots lining the walls and radiating from 
the center of one of the zoecia. The latter may represent perforations in the 
diaphragms.* 
The surface and growth of this species remind one of species of Fistulipora with 
small zocecia. The laminar form of the zoaria will, it is believed, effectually distin- 
guish it from other forms of Nicholsonella. I know of no associated bryozoan with 
which it might be confounded, and the mere mention of caution should deter the 
student from carelessly classifying the Nicholsonella with the very different discoidal 
species of Prasopora and Mesotrypa. 
Formation and locality—Rare in the middle third of the Trenton shales at St. Paul and Min- 
neapolis. : 
*Such pore-like “dots” and other minute unexplained structures have been drawn carefully on a number of the plates 
attached to this work. Some day perhaps we may be able to appreciate their significance. In the meantime we must 
gather facts and I shall continue to delineate them as faithfully as I can. In this coanection it may be well to mention wha} 
many microscopists have long observed with dismay. Namely, that minute structures like those in question are gradually 
obliterated by some insidious action of the Canada balsam in which the preparations are mounted. It is therefore desirable, 
indeed necessary, to make the drawings as soon as possible after mounting the sections. 
