94 
SHELL GALLEKY. 
lid is open. The Mediterranean species B. caUense (Fig. 13) grows 
attached to the rocks. The little exhibited specimen is on a fragment 
Fig. 13. 
Hhodosoma calleme, x 10. A, " valve " open ; B, shut. 
a, branchial ; b, atrial orifice. (After Lacaze Duthiers.) 
of shell in front of a black patch. ; The figure shows specimens with 
the lid open and closed. 
Family Clavelinidw. The body is attached to a creeping 
stolon or mass of stolons, from which new individuals arise by 
budding. The other three families of Simple Ascidians included 
solitary forms, but the Clavelinidae are social, and form colonies 
wherein each individual has its own test. 
Clavelina lepadiformis (Fig. 14) forms graceful crystal vases about 
an inch in height. The figure shows one individual, but usually 
the processes at the base extend out as stolons whence other 
individuals arise. 
Diazona violacea, from Cornwall, forms beautiful purple disk- 
shaped colonies in which the ascidiozooids arise from a basal mass 
of stolons. Sometimes the ascidiozooids die down, leaving only a 
smooth violet pad, which in due time produces a new crop of ascidio- 
zooids. 
