98 THE PALEONTOLOGY OF MINNESOTA. 



[Introduction. 



TERMINOLOGY. 



ZOARIUM (=polyzoarium and coencecium auctt.): The composite structure formed 

 by repeated gemmation. 



ZofficiuM (=cell auctt.): The true cell or chamber in which the polypide is 

 lodged. 



MBSOPOEES (= interstitial cells auctt.): -The -angular or irregular cells which 

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

 Crfjptostomata, 



VESICULAR TISSUE : The vesicles which occupy the space between the zooecia 

 in Pachydictya, the Fistuliporida? and other paleozoic Bryozoa. 



ACANTHOPOKES (=^spiniform corallites Nicholson, spiniform tubtili Ulrich, Wand- 

 rohrchen Dybows,ki) : The tubular spines which are found in so many paleozoic 

 Bryozoa, notably Dekayia, Leioclema and Batostoma. 



MEDIAN Ti\jv\jLi(Wcindstr<inge Dybowski): Very slender tubes which are present 

 between the zooecial walls and the median lamina? of certain double leaved forms 

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

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

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



COMMUNICATION PORES : Small pares which pass through the walls of the zocecia 

 and establish communication between adjacent cells. 



OCECIUM (=ovicell, gonocyst, goncecium 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 (=tabul(e 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). 



Zo(EciAL COVERS (opercula) 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 laminar 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. 



