204 CHAETODERMA SQUAMOSUM. 



The openings of the coelomoducts into the pericardium occur slightly behind 

 the level of the posterior dorsal commissure. From this point the dorsal section 

 of each of the ducts extends anteriorly and unites with the mid section of the 

 main portion of the organ. This main, glandular or ventral section is character- 

 ized by great simpUcity. Faint lobes occur in its walls accentuated by a very 

 few internal septa. 



The nervous system is normal in all of its essential features. 



Chaetoderma squamosum, sp. nov. 



A single specimen (Plate 11, fig. 5) of this species was dredged at a depth 

 of 1,234 fathoms (Sta. 2534A) about 200 miles southeast of Cape Cod, Massa- 

 chusetts. The total length of the body was 25.7 mm. vnth a width of 1.3 mm. 

 in the prothorax and of 1.2 mm. and 1.7 mm. through the metathorax and 

 abdomen respectively. The color is grayish white due in part to a grayish 

 colored incrustation particularly over the pro- and metathorax and to the 

 lead colored liver partially visible through the translucent body wall and over 

 Ijdng spicules. The buccal sensory plate, roughly elliptical in outline, is some- 

 what concealed in the semicircular groove; it is apparent, however, that the 

 mouth opening is comparatively small and is entirely surrounded by the plate. 



In the neighborhood of the junction of the pro- and metathorax the spines 

 (Plate 11, fig. 9) measure from 0.11 to 0.19 mm., and are further characterized 

 by unusual thinness and the absence of a sharply defined keel. The hypodermis 

 (Plate 13, fig. 7) lacks any distinguishing features. In many places, especially 

 in the anterior end of the body, the nuclei are arranged in two or three layers 

 although the cells to which they belong may actually constitute a single layer. 

 Occasionally the more external nuclei are spindle-shaped, but it is not certain that 

 this characteristic is correlated with any especial function. The nuclei of the 

 spicule-matrix cells are conspicuous objects, nearly twice the size of the ordinary 

 hypodermal nuclei, and are further distinguished by staining a hghter shade. 



The buccal plate comprises a thick, external cuticular plate secreted by 

 the underlying hypodermis whose cell boundaries are very difficult to deter- 

 mine. For this reason it is impossible in the present instance to accurately 

 relate these elements to the numerous nerve and muscle fibres and to the duc- 

 tules of deep seated gland cells. Generally speaking the hypodermal cells are 

 relatively slender, often unusually high in the vicinity of the mouth and at 

 various places muscle cells appear to pass between them to attach to the cutic- 

 ular plate, while nerve fibres have been undoubtedly seen to attach to the bases 

 of a few cells with spindle-shaped subcentral nuclei. The ductules perforating 



