Primitive Type of Compound Ascidian. 



2G7 



Musculature in tlie tlioracic region consisting of both longi- 

 tudinal and transverse bundles. Oviduct and vas deferens 

 present in mature zooids. No incubatory diverticulum of the 

 cloaca. 



Fig. 1. 



Archidistoma aggreyatum. — A small colony, enlarged. 

 Fig:. 2. 



'-^" 



£y 



X*' 



Archidistoma aggregatum. — Part of another colony, enlarged, showing the 

 partial fi-eedom of the zooids of a clump, and the tendency of the 

 cloacal openings towards a central position. 



Archidistoma aggregatum, sp. no v. 



Clumps composed of a small but variable number of zooids. 

 Test arenaceous. Tentacles about thirty in number. Pharynx 

 possessing three rows of straight elongated stigmata ; hori- 

 zontal membranes between the rows of stigmata ; no inter- 

 mediate supporting membranes. Ova large, containing much 

 food-yolk. 



Archidistoma aggregatum is a connecting-link between the 

 true Distomidffi [Distoma, Cystodites, Distaplia, Oxycoryniay 



18* 



