442 Viiiversitij of Calif ornia Puhlications in Zoology [Vol.16 



Genus 2. Halocynthia (Pyura, some authors) 



Body mostly approaching globular, always firmly attached, sometimes short- 

 pedunculate; surface usually free from foreign substances but often bearing 

 processes of various kinds; both orifices 4-lobed. 



Outer coat (test) usually leathery, rather cartilaginous and semitransparent. 



Branchial tentacles always compound. 



Branchial sac with folds, usually well developed; prevalent number from four 

 to seven, but a few species with a smaller number and a. few with as many as 

 fifteen; dorsal lamina always with processes or languets. 



Intestine on the left side, forming a wide loop. 



Sexual orgatis on both sides. 



Genus 3. Styela (Tethjrum, some authors) 



Body attached, not infrequently pedunculate, sometimes coated with sand; 

 both orifices 4-lobed, often inconspicuously so. 



Outer coat leathery, usually thin, surface typically unarmed. 



Tentacles both branchial and atrial present, both kinds simple, branchial 

 larger. 



Branchial sac with four folds on each side, some 'of which may be much 

 reduced in size. 



Intestine on left side, stomach frequently long with narrow folds in the wall. 



Sexual organs on both sides, ovary typically in several sausage-shaped masses 

 with the testes arranged about them in smaller lobes. 



Genus 4. Ascidia (Phallusia, some authors) 



Body attached, almost always sessile, surface usually smooth and free from 

 foreign substances; branchial orifice 8-lobed, atrial 6-lobed. 



Outer coat usually transparent or nearly so, soft or cartilaginous. 



Branchial tentacles simple, usually numerous and slender. 



Branchial sac never with prominent folds, but often with many small plica- 

 tions; papillae on the inner surface at the intersections of the longitudinal and 

 transverse vessels; dorsal lamina a membrane extending behind the esophageal 

 opening. 



Intestine on the left side. 



Sexual glands situated within the intestinal loop. 



Benal vesicles present, numerous, confined to the wall of the intestine. 



Genus 5. Chelyosoma 



Body flattened from above, the upper surface covered with tortoise-shell- 

 like plates; both orifices 6-lobed. 



Outer coat cartilage-like, translucent, the anterior part differentiated into 

 horny plates. 



Branchial sac, general t3'pe that of Ascidia and Ciona. but stigmata strongly 

 curved or coiled; dorsal languets as in Ciona. 



Intestine located ventrally, sometimes to the right, sometimes to the left; 

 stomach wall, in part, chambered. 



Sexual organs forming a network on the intestinal loop. 



Genus 6. Ciona. 

 Body cylindrical, attached; branchial orifice 8-lobed, atrial 6-lobed, lobes not 

 prominent. 



Outer coat thin, transparent, soft. 

 Branchial tentacles simple, slender. 



