CLASSIFICATIOlSr 01" THE TUNICATA. 635 



Family VII. POLTSTYELID^, Herdman, 1886. 



Colomj massive or incrusting, sessile, rarely pedimculated, or 

 formed of small masses connected by stolons. No common 

 cloacal cavities present. 



Ascidiozooids large and usually sliort-bodied, rarely witli a 

 distinct abdomen. Both apertures 4i-lobed, and opening directly 

 to tlie exterior. 



Test firm and cartilaginous. Matrix generally fibrillated, test- 

 cells small and inconspicuous, bladder-cells rarely or never 

 present. Vessels abundant, branched, and provided with dis- 

 tinct terminal bulbs. 



Branchial sac large and well developed. Folds sometimes 

 present. Internal longitudinal bars strong and fairly numerous. 



JDorsal lamina in the form of a plain membrane. 



Tentacles numerous, simple. 



Alimentary canal usually placed alongside the branchial sac, 

 rarely extending beyond it posteriorly. 



Gonads in th^ form of polycarps attached to, or imbedded in, 

 the mantle, and projecting into the peribranchial cavity. 



Gemmation effected by means of the vascular prolongations 

 from the ascidiozooids into the common test (?). 



The genera which have been referred to this family may be 

 distinguished as follows : — 



/Ascidiozooids projecting above surface of colony 1 



[Ascidiozooids completely embedded in common test 2 



, I Abdomen as long as the thorax Thylacium. 



i No abdomen present Polystyela. 



q f Colony formed of small masses iinited by stolons. Chorizocormus. 



"" I Colony not broken up into masses and stolons 3 



q I Colony thick and massive 4 



I Colony thin and incrusting Synstyela. 



. / Test incrusted with sand Oculinaria*. 



I Test not (or very slightly) incrusted with sand Goodsiria. 



Thylacium, Cams, 1850. 



Colony formed of individuals projecting from a common fleshy 

 base. 



* This genus is only imperfectly known. The description is insufficient. 



