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



The Test is cartilaginous, but thin and almost membranous; it is slightly thickened 

 alung; the dorsal edge ; it is soft and easily torn, and is semi-transparent. 



The Mantle is thin a. id membranous ; it adheres closely to the inner surface of the test. 

 The musculature is feeble ; the bands are light brown in colour, but are narrow and distant. 



Tlie Branchial Sac is not folded ; it is thin, but of moderate strength on account of the 

 small size of the stigmata. The vessels form a close irregular network. The stigmata are 

 small and circular, or polygonal, and have no definite arrangement, 



The Endostyle is narrow. It is not prominent, but distinct, and extends down to the 

 ventral edge of the narrow posterior end of the sac, and then turns and ascends the dorsal 

 edge, as far as the oesophageal aperture, which is situated about half-way up the sac. 



The Dorsal Lamina is a very narrow plain membrane, with no folds nor thickenings. 



The Dorsal Tubercle is elongated antero-posteriorly ; it is placed near the atrial 

 aperture ; the right horn is large, and is curved outwards to the right. 



The Nerve Ganglion is small, oval, and placed a little way posterior to the dorsal 

 tubercle ; it has the rounded neural gland rather on its right side. 



The Viscera. — The intestine and genitalia form an elongated compact mass along the 

 dorsal edge of the branchial sac. 



This interesting specimen was in such bad condition that at first sight it seemed like a 

 confused mass of lacerated and entangled membranes. It has evidently been torn from 

 end to end along the right side, and part of the mantle and branchial sac are entirely 

 gone, while what remains is in parts displaced and hanging in shreds. Consequently it 

 has been impossible to give the external form with precision, and no trace of the tentacles 

 has been discovered. 



The external shape is more or less pyriform, with the anterior end wide and the 

 posterior narrow, and produced to form a short peduncle (PI. XXXVII. fig. 6). The 

 apertures are placed at the extremities of the anterior end, and are large circular holes 

 apparently not lobed. The test is thin and soft, It is slightly thickened along the 

 dorsal edge, forming a pad over the viscera corresponding to the plates (fig. 2, t.t.) in 

 the last species, but no cartilaginous nodules are present, It is not modified in any way 

 on the peduncle. 



The mantle has a few narrow light brown muscular bands running chiefly longitudi- 

 nally along the middle of each side. There are none down the dorsal and ventral edges. 

 They are not crumpled as in the mantle of the last species (compare figs. 3 and 9 on 

 PL XXXVII.) , and the arrangement is very suggestive of the musculature of some of the 

 Clavelinidae. 



The branchial sac (PL XXXVII. fig. 7) is veiy simple, being formed by a network of 

 vessels, all similar, and having no symmetrical arrangement. There are no folds, and no 

 internal longitudinal bars. 



