628 PEOF. "W. A. HEED man's EETISED 



from the north coast of France and the Mediterranean, which 

 has several varieties, differing from one another in the degree of 

 concrescence between the ascidiozooids and systems and lobes of 

 the colony. 



Unrecognizdhle Polyclinidce. 



Amaroiicium glahrum, Verr. (E. N. Am.) 

 A. pallidum, 'Y err. (E.N.Am.) 

 A. 'pellucidum, Yerr. (E. N. Am.) 

 A.stellatum, Verr. (E. N. Am.) 

 A. constellatum, Verr. (E. N. Am.) 

 A. pomum (?). (N.W. Eur.) 

 A. papillosum, Aid. (N.W. Eur.) 

 A. simulans, Giard. (N.W. Eur.) 

 Aplidium nutans, Johnst, (N.W. Eur.) 

 Macroclinum crater, Verr. (E. N. Am.) 

 Polyclinum succinemn. Aid. (N.W. Eur.) 

 P. cerebriforme, Aid. (N.W. Eur.) 



Family lY. DIDEMNID^, Giard, 1872. 



Colony usually flat, thin, and incrusting, rarely thick and 

 massive, never pedunculated. 



Systems complicated and irregular, inconspicuous or absent. 

 Common cloacal apertures usually conspicuous. 



Ascidiozooids rather small, divided into two regions — thorax 

 and abdomen. Branchial aperture 6-lobed ; atrial plain or pro- 

 vided with an atrial languet. 



Test gelatinous or cartilaginous, usually containing stellate 

 calcareous spicules. Ectodermal processes well developed, and 

 provided with muscle-fibres so as to form retractor muscles. 



Branchial sac small and not well developed. Eows of stigmata 

 few, usually three or four (rarely six). 



Alimentary canal united to thorax by a narrow neck. Stomach 

 usually smooth-walled. 



Gonads placed alongside the intestinal loop. Ovary very 

 simple ; ova large. Male system consisting of a single large 

 testis, around which the first part of the vas deferens is coiled 

 spirally. 



Gemmation from the pyloric region ; thorax and abdomen of 

 the new ascidiozooid formed from separate buds. Embryonic 

 blastogenesis rudimentary only. 



