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 arhorea, from 

 higher rocks, is strikingly like N. pulchra superficially. 



Formation and locality.— TSoi uncommon in the "Pierce limestone" at Murtreesboro, Tennessee, 

 where it is associated with an abundance of fossils, chiefly Bryozoa. 



Mu8. Reg. No. 8131. 



NiCHOLSONELLA LAMINATA, M. 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 maculae or areas in 

 which the interspaces between the zocecia are wider than usual. Zocecial apertures 

 circular, regularly arranged, nine or ten in 3 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 zooecia. 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 zooecia. 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 snnA Mesotrypa. 



Formation and locality.— B.3,Te in the middle third of the Trenton shales at St. Paul and Min- 

 neapolis. 



»9 h Dore-like "dots" and other minute unexplained structures have been drawn carefully on a number of the plates 

 h'rt t this work Some day perhaps we may be able to appreciate their significance. In the meantime we must 

 attached to shall continue to delineate them as faithfully as I can. In this connection it may be well to mention wha; 



gather, octe ^" ^^^^ j^^^ observed with dismay. Namely, that minute structures like those in question are gradually 



many mlcrosoop , ,^, action of the Canada balsam In which the preparations are mounted. It is therefore desirable, 

 rn^eeltlL'a^rto ml^trdCln^ as soon as possible after mounting the sections. 



