BRYOZOA. 295 



growth is represented by many species of Fistulipora, Monticuli- 

 pora cincinnatiensis Nicholson, and several species of Steno- 

 pora. 



3. The massive zoarium, which may be free, attached only at 

 the base, or growing around some foreign body. The zooecia 

 form long tubes, divided at more or less frequent intervals by 

 diaphragms. The massive zoarium is seen in Monticulipora 

 mammulata D'Orbigny, some species of Leptotrypa, Mono- 

 trypa, Fistulipora and Crepipora. 



4. The discoid zoarium has the form of a plano-convex or 

 concavo-convex disc. Generally the convex surface is cellulifer- 

 ous and the flat or concave surface covered Avith a striated and 

 wrinkled epitheca. Monotrypa? petasiformis Nicholson, Lepto- 

 trypa discoidea Nich., Diplotrypa petropolitana Pander, and 

 Prasopora lycoperdou are examples. More rarely the upper or 

 celluliferous surface is concave or flat, and the lower side con- 

 vex. Of this condition Scenellopora radiata, and Proutella dis- 

 coidea (Prout sp.) examples. The same type of zoarium per- 

 tains to species of Aspidopora, Discotrypa and Cyclopora, but 

 in these the height when compared with the width is propor- 

 tionately much less than in the examples first cited. In all, 

 the adult form was essentially free, but that the majority were 

 originally attached to some small foreign body usually admits 

 of demonstration. 



5. The bifoliate zoarium, in which the zooecia diverge from a 

 double median lamina or basal plate, and open upon the two 

 surfaces of a foliate expansion, or of flattened branches. This 

 type of grow r th is very common, being characteristic of the 

 PTILODICTYOXID.E and STICTOPORID.E. Among the CYSTODICTYO- 

 NID.E, Prismopora, Glyptopora and Evactinopora offer peculiar 

 modifications of this type of growth. 



6. The dendroid or ramose zoarium, in which the entire free 

 surface is covered by the apertures of zooecial tubes, is very 

 common among the TREPOSTOMATA. The tubes radiate in all 

 directions from an imaginary axis, or from an axial tube. A 

 ramose zoarium is seen in Rhombopora, Batostomella, Am- 

 plexopora, Monotrypella, Diamesopora, Nematopora, etc., etc. 



