580 PEOF. w. A. herdman's eeyised 



The three species may be separated as follows : — 



(With one large fold on left side of branchial sac ; body ovate. 

 B. ndrabilis, Herdm. (Southern Oc.) 

 With small folds only 1 



, r Body discoid 5. (^zsco?«Zots, Herdm. (N. Pac.) 



I Body globular B. minutus, Kerdm. (N. Pac.) 



Sttela, MacLeay^ 1824. 



^ody attached, sessile, rarely pedunculated, sometimes in- 

 crusted with sand. Apertures both 4-lobed. 



Test usually thin, coriaceous. 



Branchial sac witJi 4, or fewer, folds on each side. 



Dorsal lamina usually with a plain margin. 



Tentacles simple, unbranched. 



Alimentary canal forming a narrow loop. 



Gonads on both sides of the body. Ovaries in the form of 

 elongated sausage-like bodies. 



The known species of Styela may be arranged as follows : — 



/Branchial folds partly rudimentary I 



I Branchial folds all well developed 2 



1 r Dorsal lamina plain 3 



\ Dorsal lamina not a plain membrane 4 



[Two or 3 distinct branchial folds on each side 5 



I Four sliffht folds on each side 6 



(Colour cream-white ; test thick but soft, scaly. 

 8. squamosa, Herdm. (A. Arct.) 

 Colour dark brown ; test tough, wrinkled. 

 8. pusilla, Herdm. (N. Pac.) 



n /Body flattish, longer than high 8. humilis, Heller. (S. Pac.) 



I Body acorn-shaped, as high as long. 8. glans, Herdm. (S. Atl.) 



{Margin of dorsal lamina crumpled 

 Margin of dorsal lamina notched and toothed. 

 *S'. fiava, Herdm. (S. Atl.) 

 {Atrial aperture far back; surface covered with silky hairs. 

 8. scricata, Herdm. (A. Arct.) 

 Atrial aperture anterior ; surface rough and slightly sandy, no hairs. 

 8. oblonga, Herdm. (S. Atl.) 



o / Body covered with sand 



[Body not covered with sand 



D /More or less sandy all over 10 



I Sand confined to posterior half 8. bicolor, Sluit. (Mai.) 



{Individuals aggregated in clusters, test coriaceous. 

 8. racemosa, n. sp. (Austr.) 

 Individuals not aggregated, test rather cartilaginous *. 

 8. exigua, Herdm. (Austr.) 



* Here also 8tyela perforata and 8tyela Traiistedti, both from the Malay 

 Archipelago, the description of which by Sluiter has reached me since this 

 table was in type, find their place ; they can be readily distinguished from 



8. exigua. 



