98 THE PALEONTOLOGY OF MINNESOTA. 



tintrodaction. 



TERMINOLOGY. 



ZoARiuM {=polyzoarium and cmnmcium auctt.): — The composite structure formed 

 by repeated gemmation. 



ZofficiUM (=ce/Z auctt. ) : — The true cell or chamber in which the polypide is 

 lodged. 



Mesopoees {=interstitial cells auctt.): — -The angular or irregular cells which 

 occupy the spaces between the zooecia in many of the Trepostomata and some of the 

 Cryptostomata, 



Vesicular Tissue : — The vesicles which occupy the space between the zooecia 

 in Pachydictya, the Fistuliporidce and other paleozoic Bryozoa. 



Acanthopoees {=spiniform corallites Nicholson, spiniform tuhuli Ulrich, Wand- 

 rohrchen Dybowski) : — The tubular spines which are found in so many paleozoic 

 Bryozoa, notably Dekayia, Leioclema and Batostoma. 



Median 'Yxs'R\si.i{Wandstrdnge Dybowski): — Very slender tubes which are present 

 between the zooecial walls and the median laminse of certain double leaved forms 

 (e. g. Bhinidictyonidce). Their apertures at the surface are slightly elevated and 

 present the appearance of series of minute granules. The small granules in Bhomb- 

 opora, Stenopora and other genera,' are supposed to be of the same character. 



Communication Pores : — Small pores which pass through the walls of the zooecia 

 and establish communication between adjacent cells. 



OcEGivM {-=ovicell, gonocyst, gonoecium auctt.): — A modified zooecium set apart for 

 reproductive functions, the inflation of the zoarium in which the embryos are devel- 

 oped, or a special receptacle (marsupium) which is attached to the zooecium, and 

 serves the same purpose. 



Diaphragms {=tabulce and septa auctt.): — The straight plates which cross the 

 tubular zooecia and mesopores in the Trepostomata and a few forms of the Crypto- 

 stomata. 



Cystiphragms : — The convex plates which line the walls of the zooecial tubes in 

 some of the Trepostomata (Prasopora). 



ZocECiAL COVERS {operculo) and Perforated diaphragms: — Horizontal plates per- 

 forated subcentrally, covering the zooecia in the Trepostomata. As growth proceeds 

 in the colony these are left behind in the tubes, and mark the successive stages. 



Hemisepta :— The superior hemiseptum is a plate or lamina^ projection within 

 the posterior border of the primitive zooecial aperture, common in the typical Cryp- 

 tostomata. The inferior hemiseptum is a similar projection on the anterior wall, or 

 on the median laminae of bifoliate forms, situated a short distance beneath the supe- 

 rior hemiseptum. One or the other, or both may be absent. 



