60 THE AUSTRALIAN MUSEUM. 



terms, Holosomata* and Merosomata, may be appropriately 

 applied. The Holosomata would comprise those forms 

 with compact bodies the Botryllidae and the Polystyelidae 

 which we believe are derived from ancestral Cynthiidae ; 

 while the Merosomata are the remaining families, with 

 more or less spread out bodies, which are more closely 

 related to the Clavelinidae. 



Section A. MEROSOMATA, Sluiter, 1895. 



Compound Ascidians in which the alimentary and repro- 

 ductive viscera lie behind the branchial sac, so as to form 

 an "Abdomen " distinct from the " Thorax." 



Of the five families in this section three the Distomidae, 

 the Polyclinidae, and the Dideninidse are represented in 

 the collection. 



Family I. DISTOMID^l (Giard, 1872), Herdm., 1885. 



Colony rounded and massive, rarely incrusting, either sessile or 

 supported on a long or short peduncle. 



Systems irregular, inconspicuous or absent. 



Ascidiozooids of moderate length, and having the body divided into 

 two regions, thorax and abdomen ; they may be provided with long 

 vascular ectodermal appendages. 



Test gelatinous or cartilaginous, often thickened at the base to form a 

 peduncle, which may be traversed by large canals containing the vascular 

 appendages of the Ascidiozooids. There are sometimes calcareous 

 spicules, which, however, are not stellate. 



Branchial sac well developed ; no internal longitudinal bars present. 



Dorsal lamina represented by a series of languets. 



Alimentary canal placed posteriorly to the branchial sac, so as to 

 form an abdomen. 



Gonads and heart in the intestinal loop, or alongside it. Spermatic 

 vesicles numerous, vas deferens straight. 



This is a large family, containing 7 genera, but only one of these, 

 Colella, is represented in the present collection. 



* Sluiter used Holosomata in a much wider sense, to include also the Simple Ascidiaus. 



