3-iO MANUAL OF THE MOLLUSCA. 



Perophora, ("Wiegm.) Lister, 1834. 



Etijm. Pera, a sac, and pharos bearing. 



Type, P. Listeri, Wiegman, PI. 24, fig. 7- 



Body pedunculated, suborbicular, compressed; thoracic region plain. 



This curious little species was discovered by Mr. J. Lister at Brighton, 

 growing on Conferva elongata. It occurs in groups consisting of several 

 individuals, each having its own heart, respiration, and system of nutrition, 

 but fixed on a peduncle that branches from a common creeping stem, and all 

 being connected by a circulation that extends throughout. (Lister). 



Jlr. Poibes has dredged it adhering to weed on the coast of Anglesey; 

 he remarks " it is beautifully transparent, appearing on the weed like little 

 specks of jelly dotted with orange and brown. When dried, as it may often 

 be met with on sea-weed cast on shore, these bodies appear like the minute 

 ova of some mollusk." According to Mr. Huxley's view this genus differs 

 Avidely from the last, being a " branchial ascidiau" whilst Clavellina is an 

 "abdominal" one. 



Syntethys, Forbes and Goodsir. 



Tyi)e, S. Hebridicus, P and G. Cronlin Id. near Applecross. 



Animals compound, gelatinous, orbicular, sessile ; individuals very pro- 

 minent, arranged sub-conceutrically in the common mass ; branchial and anal 

 orifices simple, not cut into rays. 



Syntethys is a Clavellina with the habit of a Dlazona. The only known 

 species forms compact greenish translucent gelatinous masses of half a foot in 

 diameter, and nearly equal height, affixed to rocks or stones by a short base. 

 The individual ascidiaus are when full grown 2 inches in length. Their 

 inner tunics are remarkably irritable, withdrawing themselves into the com- 

 mon mass when pinched. {Forbes, Brit. Moll, iv., 244). 



FAMILY III. BoTRYLLiDAE, Compound Ascidiaus. 



Animals compound, fixed, their tests fused, forming a common mass in 

 which they are imbedded in one or more groups ; individuals not connected 

 by any internal union ; oviparous and gemmiparous, 



Milne-Edwards divides the compound ascidiaus into three tribes : — 



1. Botryllina. Individuals united in systems around common excretory 

 cavities {cloacae). Thorax and abdomen not distinct. 



2. Bidemnina. Thorax and abdomen distinct. 



3. Volyclinina. Body divided into three distinct portions— I, thorax, 

 with the branchial apparatus; — 2, superior abdomen with the digestive organs ; 

 —3, post-abdomen, containing the heart and reproductive organs. 



