220 THE VOYAGE OF H.M.S. CHALLENGER. 



lower end, and longitudinally plicated. The transverse vessels are narrow, and all of 

 much the same size. The internal longitudinal bars are strong, and the papillae are 

 large, but of one size only. The meshes are square, and contain each three or four 

 stigmata. 



Tie Endostyle is conspicuous, and terminates at the base of the ventral edge of the sac. 



The Dorsal Lamina is closely ribbed transversely, and the margin is bluntly serrated. 



The Tentacles are very numerous and crowded ; they are long and slender, varying 

 in thickness, but all of much the same length. 



Tie Dorsal Tubercle is very comjjlicated, and occupies a deep triangular perituber- 

 cular area. It forms an irregularly curved and coiled pattern, with no obvious horns. 



This is a very remarkable species, and in external appearance (Plate XXXIV. figs. 

 1 and 2) is distinctly pyriform. The dimensions given above are those of the smaller 

 specimen; the other one measures 7 '5 cm. in length, and 4 cm. in breadth; it has 

 several Ascidians and a few other animals adhering to its test. 



The greater part of the test is remarkably thin and easily torn ; on the elevated ridge, 

 however, between the siphons (PL XXXIV. figs 1 and 2), it is very thick. In one of the 

 specimens a Crenella was found imbedded in this part of the test. 



The body, when removed from the test, has a most characteristic appearance (PL 

 XXXIV. fig. 3). The siphons are long, narrow, and echinated, the branchial measuring 

 1*2 cm., and the atrial 0"8 cm. in the smaller specimen, while in the larger they are 1*8 cm. 

 and 1"4 cm. respectively. 



On the right side of the body there is a " branchial area," defined by the extension of 

 the mantle into a sort of free crenated border, the points between the crenations being 

 produced into longer or shorter sharp processes. The ventral part of this branchial area is 

 raised into a smooth rounded pad (PL XXXIV. fig. 3). This, at the anterior end, joins an 

 irregular collar which surrounds the base of the branchial siphon, and is continued as a 

 crested ridge along the dorsal edge to the base of the atrial siphon, lying under the 

 prominent ridge which was noticed as running between the two siphons in the description 

 of the external appearance. The large, globular, visceral side, when viewed from the 

 right, appears outside the branchial area dorsally, and more especially ventrally. 



The plication of the branchial sac is not well marked, and produces, as seen from 

 the inside (PL XXXIV. fig. 4), merely a little irregularity in the position and direction of 

 the interstigmatic vessels. The slanting direction in which the transverse vessels run in 

 the part of the branchial sac figured (fig. 4) is not constant, but was observed in one part 

 of the branchial sac. 



The condition of the dorsal tubercle is very remarkable. The peritubercular area is 

 triangular and deep, and its cavity is entirely occupied by a convoluted dark marking 

 (PL XXXIV. fig. 5, d.t.), which appears to represent the dorsal tubercle. The 



