EXPLANATION OF PLATE. 



Fig. 1. Diagram of a cyclostomatous polyzoon. 



2. Diagram of a cheilostomatous polyzoon (after Busk). 



3. Diagram of a pedunculate aviculariiiin (after Busk). 



4. Diagram of a sessile avicularium (after Busk). 



5. Diagram of an ascidian (after Woodward). 



(a.) Oral aperture. 

 (b.) Atrial aperture. 



6. Diagram of a cheilostomatous polyzoou (after Busk). 



(a.) Immersed avicularium. 

 (b.) Ovicell. 



7. Back view of Ommast-rephes sloanii. (No. 5, p. 3.) 



(a.) Tentacular arm. 

 (b.) Suckers or cups. 



8. Triton acclivis. (No. 33, p. 13.) 



(a.) Columella, or inner lip. 



(b.) Body whorl. 



(c.) Spire. 



(d.) Apex. 



(e.) Posterior canal. 



(_/.) Anterior canal. 



(ff.) Outer or right lip. 



(A.) Suture. 



9. Dorsal view of Terebratella cruenta. (No. 2, p. 85.) 



(a.) Foramen. 

 (ft.) Deltidium. 



10. Interior view of right valve of CMone stuchbtiryi. (No. 62, p. 70.) 

 (a.) Pallial line, 

 (ft.) Pallial sinus, 

 (c.) Adductor impressions. 

 (d.) Umbo. 

 (e.) Anterior end. 

 (f.) Posterior end. 

 Lunule. 



