68 CHAETODERMA ROBUSTA. 



tively large pores into the pericardium and as moderately spacious tubes without 

 any marked convolutions, extend to their openings into the cloaca (Plate 30, 

 fig. 7). Surrounding these pores the cloacal epithelium is modified to form the 

 glandular area similar to that of C. attenuata. 



Chaetoderma robusta, sp. no v. 



Four specimens of this species were taken south of the Alaskan peninsula 

 (Sta. 3210) in green mud at a depth of 483 fathoms. The largest specimen 

 (Plate 4, fig. 5) is 60 mm. long with an average diameter through the metathorax 

 and preabdomen of 3.5 and 4.7 mm. respectively. The smallest is 35 mm. long 

 with an average metathorax diameter of 2 mm. and 3 through the preabdomen. 

 Where the spines have not been dislodged the general color of the body is slaty 

 gray shading to buff at the anterior end of the body. A yellowish brown sub- 

 stance incrusts the spines about the cloaca. 



The hypodermis consists of numerous small cells rather closely crowded so 

 that the cells lack distinctness. However giant cells are visible and faint fibres, 

 connective tissue or muscle, springing from the underlying body wall appear to 

 attach to them. Spicule-matrix cells in all stages of development are visible, 

 and in each case the spines are attached to only one cell so far as it is possible 

 to judge. The reinaining elements are comparatively slender, compact and lack 

 any noteworthy features. The spines are represented in Plate 37, fig. 4. 



The buccal plate is shield-shaped in outline (Plate 4, fig. 19), and is pierced 

 by the mouth opening. The buccal and pharyngeal cavities are slender, and the 

 Walls of more than average thickness (Plate 30). The lining cells are accordingly 

 very slender, ciliated and are thrown into a few prominent folds. The ductules 

 of a very large number of salivary glands make their way between the cells and 

 in some cases are in the act of pouring their secretion into the canal. A sub- 

 radular system is present, and as usual two nerves are distributed to a median 

 fold of pharyngeal epithelium that probably functions as a subradular organ. 

 However with the exception of affording scarcely any outlet for the salivary 

 glands its cells are not clearly distinguishable from the general epithelium. 

 The radula consists of the usual conical tooth, rather heavier than usual, but 

 with supports and musculature of the customary type. Beyond the radula the 

 tract becomes circular in cross section before uniting with the stomach whose 

 relations to the liver and intestine are typical. 



The circulatory system presents no noteworthy features beyond the fact 

 that the heart is suspended by a fold of the pericardial wall reinforced by a few 



