120 



DISCOVERY REPORTS 



Falkland Islands, 82-80 m. St. WS 84: Falkland Islands, 75-74 m. St. WS 89: Tierra del Fuego, 

 23-21 m. St. WS 90: Patagonian Shelf, 82-81 m. St. WS 788: Patagonian Shelf, 82-88 m. St. WS 

 811: Patagonian Shelf, 99 m. St. WS 834: Patagonian Shelf, 27-28 m. St. WS852: Patagonian 

 Shelf, 86-88 m. 



External appearance (Text-fig. 47 A; PI. IV, fig. 6). The general appearance of this species is 

 already well known. In almost all the ' Discovery ' specimens the point of origin of the stalk is at the 

 anterior ventral part of the body, but in some small ones it is mid-ventral. The proportion of body 



2.0 cm 



2.0 cm 



V//&///S 



Text-fig. 47. Pyura legumen (Lesson) (St. 57) : A, intact specimen; B, test-spine; C, part of dorsal lamina. Pyura georgiana 

 Michaelsen (St. MS 14): D, intact specimen; E, test-spine; F, part of dorsal lamina. Pyura bouvetensis (Michaelsen) (St. 181): 

 G, intact specimen; H, test-spines; J, probable attitude in life with body resting lightly on the bottom. 



length to stalk length bears no direct relation to the total size of the animal, that is, to its age (see 

 Text-fig. 48). Irregular longitudinal furrows mark the surface, and in some animals these break the 

 test into rectangular or polygonal areas each bearing a group of spines. The degree to which spines 

 are developed is very variable. They may be numerous and short, forming a kind of fur, or few and 

 scattered. When well developed the spines reach 2 mm. in length, are sharply pointed, and bear small 

 thorn-like processes (Text-fig. 47 B). 



Atrial organs. The three pads, called atrial organs, which lie within the atrial siphon, at its base, 

 have been noticed by several workers, especially Michaelsen (1900) and Arnback (1938). The structure 

 and function of the organs, however, have never been clarified. Sections show that the atrial organs 

 are thick pads of test substance richly provided with blood spaces. As these spaces are lined with 



