NORTH AMERICAN EARLY TERTIAEY BRYOZOA. 701 



FIG. 230. Family Crisiidae Johnston, 1847. 



A-G. Crisia ebiirnea Ellis, 1755. A. Larva seen in profile. B. Aboral pole of larva. C. Oral 

 pole. (A-C after Barrois, 1877.) CD, digestive cavity; s, oral face or from the vestibule. D. E, 

 F. Embryos (after Smitt, 1865). G. Ovicell showing internal sac containing the primary em- 

 bryos (after Smitt, 1S65). 



H-M. Crisia dcnticulata Milne-Edwards. 1838. H. Section of a primary embryo. Two of . 



the lobes of this embryo are provided with a central cavity and the two cellular distinct layers. 

 The constriction which must cause the separation of the rest of the embryos is rather marked. I, 

 J, K, L. Meridian sections showing different stages in the development of the secondary embryo. M. 

 Sagittal section of an ovicell inclosing two primary embryos and a rather large number of sec- 

 ondary embryos, cal, calotte; cce, external cellular layer of the secondary embryos; cci, internal 

 cellular layer of the secondary embryo : co. coronna ; eb, primary embryo ; 662, secondary embryo ; 

 ect' ect", the two cuticular leaves of the ectocyst; ect a, aboral ectocyst; ecto, oral ectocyst; ep, 

 endocys ; gt, tentacular sheath; one, central nervous organ of the embryo; o, orifice; p, pores; si, 

 internal sac ; tm, mesenchymatous tissue ; va, valvule. 



N. Crisidia (Crisia) franciscana Robertson, 1910. Cross section of an ovicell in an older 

 stage of growth showing a relatively large embryo (emb.) and a septum (sep) whose growth is 

 about completed. The chitinous tube (clii. t) growing down into the ooecial cone (oe. c) shows 

 only at intervals in this section. 



O. A cross section of an ovicell containing a developing embryo on a young stage (emb) and 

 showing, also, an early stage in the growth of the septum (sep). 



P. Crisia edwardsiana D'Orbigny, 1839. Diagrammatic representation of a cross-section of 

 the ovicell showing the cellular septum (scp) with the chitinous tube (chi. t) and chitinous floor 

 (chi. fl). (O, P. After Robertson, 1910.) 



Q-S. Crisia ramosa Harrner, 1891. Sketches showing development of ovicell. The ovicell 

 has in each case been numbered 4 in order to admit of ready comparison between the three stages. 



T. Crisia, eburnca Ellis, 1755. A young internode decalcified, with a developing ovicell. 

 (Q-T after Harmer, 1893.) A. B, O. Summits of an imaginary triangle. 



