DESCRIPTION OF THE SPECIES 9 



Muscle fibres. Mean number 29-4± 1-4 for M. IV, based on forty-eight specimens. See pp. 15- 

 21 for explanation. 



Alimentary canal. Compact, oval nucleus. 



Stolon. Proceeds forward, turning left at about the level of M. Ill, to proceed back emerging from 

 the test in front of the nucleus. 



Length. Up to 45 mm. 



Text-fig. I. S. fusiformis (a) Solitary form, ventral view. Length 20 mm. (b) Aggregate form, dorsal view. 



Length 20 mm. (From Thompson, 1948.) 



Aggregate Form (Text-fig. ib) 

 (Based on the examination of forty-eight specimens) 



External appearance. Body barrel shaped with conical anterior and posterior protuberances of 

 the test which are typically long in relation to the body, giving it a slight asymmetry* and an elongate, 

 fusiformis appearance. 



Test. Smooth, firm, transparent with no obvious ridges. 



Body muscles. Six body muscles. M. I-IV and M. V-VI fuse dorsally, thus forming two groups. 

 M. IV-V approach and join laterally. 



Muscle fibres. Mean number 51 -8 ±1-4 for the total of M. I-VI, based on 45 specimens. See 

 pp. 15-21 for explanation. Approximate mean number of fibres per muscle of 8-6. 



Alimentary canal. Compact, oval nucleus with its major axis lying to the right. Pale green in 

 living specimens. 



* Note. In S. fusiformis and in the three other species to be described the protuberances or processes of the test are 

 asymmetrical, the anterior being to the right, the posterior to the left, or vice versa depending on the zooid's original 

 position in the stolon. 



