378 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1920. 



EXPLANATION OF PLATES. 



PLATE 1. 



Fig. 1. — Limestone slab, natural size, composed mainly of Trepostomata or 

 stony bryozoa. Middle Ordovician, St. Paul, Minnesota. 



Fig. 2. — Surface of limestone, x 2, from tbe Lower Carboniferous (Warsaw) 

 limestone at Columbia, Illinois, exhibiting the remains of 'lacelike bryozoa 

 (Fenestella and Polypora) of tbe order Cryptostomata. 



Plate 2. 



Fig. 1. — Bryozoan marl from the Early Tertiary rocks of South Carolina. 

 The figure to the left (x2) represents the rock as exposed by weathering and 

 the one to the right the appearance of the specimens (x 2) after preparation 

 for study. 



Fig. 2 — Dredgings from the vicinity of the Philippine Islands showing various 

 types of recent cheilostomatous bryozoa, natural size, in a more or less frag- 

 mentary state. 



Plate 3. 



Growth forms in the Cyclostomata. 



Fig. 1. — A typical encrusting linear species Stomatopora pratti Canu and 

 Bassler, x 4, from the Eocene (Jacksonian) of North Carolina. A second, very 

 minute, species of Stomatopora is also present. 



Fig. 2. — Portion of the zoarium of Stomatopora polygona Canu and Bassler, 

 x 4, illustrating tendency of the branches to form polygons. 



Fig. 3. — A fragment of Early Silurian stony bryozoa (Cryptostomata) with 

 an encrusting cyclostomatous species, Corynotrypa turgida Ulrich, and the 

 latter magnified, x 6, to show the curious club-shaped zooecia. 



Fig. 4. — Another species of encrusting Cyclostomata, Corynotrypa inflata Hall, 

 x 6, introduced for comparison with the preceding to show how these simple 

 species differ from each other. 



Fig. 5. — A common, recent bryozoan, Crista, magnified, consisting of erect 

 tuftlike zoaria made up of articulated segments with the zooecia arranged in 

 two rows. The prominent ovicell is present. 



Fig. 6. — Another recent jointed bryozoan, Crisidia cornuta Ellis, x 16, with 

 uniserial zooecia. 



Fig. 7. — Noncelluliferous side of an erect, much-branched zoarium, Horn&ra 

 frondiculata Lamouroux, from the recent seas. 



Fig. 8. — Celluliferous side of Discosparsa marginata D'Orbigny, magnified, 

 from the Cretaceous of France, showing subcolonies in various stages of growth. 



Fig. 9. — A pear-shaped zoarium, Lichenopora franqana D'Orbigny, magnified, 

 from the Cretaceous rocks of France. 



Fig. 10. — A recent fungiform bryozoan, Fasciculipora ramosa D'Orbigny, 

 from South Patagonia, slightly magnified. 



Fig. 11. — Lateral view of Idmonea magnireversa Canu and Bassler, x 8, from 

 the Eocene (Jacksonian) of North Carolina, showing the zooecial openings 

 on one side of the branch only. 



Fig. 12. — Another branching species, Mecynoccia cylmdriea Canu and Bassler, 

 x 8, from the Eocene rocks of North Carolina, in which the apertures open on all 

 sides of the zoarium. 



