646 PROF. w. A. heedman's eevised 



Branchial sac opening freely into the peribranchial cavity ; 

 no lateral walls ; at most some rudimentary stigmata along dorsal 

 edge. 



Dorsal lamina in the form of a vascular band marking the 

 junction of branchial and atrial sacs. 



Alimentary canal coiled up to form a small opaque mass placed 

 posteriorly and ventrally, and usually known as the " nucleus." 



Chain of aggregated forms in the shape of an elongated ribbon- 

 like band. 



One embryo developed at a time, and covered. 



This genus has had a number of species referred to it, amongst 

 which the foUowiug are sufficiently known to be distinguished : — 



' Aggregate forms with only 4 transverse muscle-bands. 



8. punctata, Forsk. (Atl., Med.) 

 Aggregate forms with 5 or 6 muscle-bands 1 



f Aggregate forms with 5 muscle-bands. 

 S. cylindrica, Ouv. (Atl., Pac, A. Arct.) 

 Aggregate forms with 6 muscle-bands 2 



(Descending branches of 4th and 5th muscles approximated on each side. 

 8. runcinata-fusiformis, Cham.-Cuv. (Atl., Med., Pac, I. O., Mai., A. Arct.) 

 Descending branches of 4th and 5th muscles not approximated. 

 8. africana-maxivia *, Forsk. (Atl., Ind. 0., Med., A. Arct.) 



The solitary form of 8. runcinata-fusiformis is easily distin- 

 guished by the short spinose projections from the posterior end ; 

 while ^S'. cylindrica and S. africana-maxima (which have no such 

 processes) differ from one another in their muscles, those of the 

 latter species being all parallel, while in 8. cylindrica the four 

 anterior approximate dorsally. 



Thalia, JBlumenhach, 1810. 



Branchial sac having only ciliated bands along its dorsal edge. 



Aliinentary canal closely coiled up to form a " nucleus." 



Oevimation results in a ribbon-like band of aggregated forms. 



8ingle embryo develops at a time. It is not covered. 



In other particulars like Salpa. 



This section includes only the species Thalia democratica- 

 mucronataf, Forsk. (Atl., Pac, Ind. O., Med., Mai., Austr.), and 

 the rajviety fagellif era, Trsiixst. (Atl. and Ind. 0.), distinguished 

 by the very long taperiug processes at the posterior end of the 

 body in the solitary form. 



* 8alpa mollis, Herdm. (S. Pac), is probably allied to this species, but 

 cannot be placed with certainty. 



t Salpa nitida, Herdm. (Pac), is probably closely related to this species. 



