196 CHAETODERMA VADORUM. 



(Sta. 20B) was dredged at a depth of 95 fms., and a third came from Cape Cod 

 Bay, Mass. (Sta. 317 sp.) at a depth of 25 fms. Two additional specimens, 

 of approximately the same size, bear the label "Casco Bay, Maine, U. S. Fish 

 Com., Aug. 5th. 1873." No other data are forthcoming but it may be assumed 

 that they are shallow water forms. The length of the largest (sectioned) speci- 

 men was 15.2 mm. with a diameter through the abdomen (Wiren) of 1.45 mm.; 

 the smaller specimen is 12.5 mm. long by 1.1 in diameter. The color is hght 

 brownish yellow though this may be due to long preservation or to tannin from 

 the cork. The buccal plate (Plate 13, fig. 2) is somewhat distorted, but appears 

 to be eUiptical in outline or broadly shield-shaped with the mouth occupying 

 a deep indentation in the dorsal two thirds. 



The spines examined were taken from the neighborhood of the union of 

 the metathorax and abdomen, and range in length from 0.1 to 0.14 mm. They 

 present the usual spearhead appearance (Plate 12, fig. 3), and are strongly keeled 

 throughout nearly their entire length. The cells composing the hypodermal 

 layer (Plate 13, fig. 8) comprise two distinct types, the matrix cells of the spic- 

 ules, and those probably responsible for the development of the cuticle. The first 

 exist in the form of flattened disc-Uke bodies attached to the basal portion of 

 the spine, and indicate that in this genus every spicule is the product of a single 

 cell. The cells of the second class possess spherical nuclei, and a columnar form 

 though as a general rule they are without clearly defined boundaries. 



In the region of the union of the pro- and metathorax especially the hj'po- 

 dermal layer is seen to rest upon a felt-work of connective-tissue fibres, forming 

 a species of basement membrane that stains intensely in haematoxylin. A 

 short distance removed from this region the meshwork becomes less compact 

 and less darkly staining. Under fairly high magnification fibres may be seen 

 to traverse the underlying somatic muscles and to enter the basement mem- 

 brane whose elements they resemble closely; but in no case have they been 

 seen to extend into the hypodermal layer, and it may be added the material 

 appears to be excellently preserved. 



As usual the buccal plate is composed of a heavy cuticular layer (Plate 13, 

 fig. 4) resting upon the hypodermis in which the cell elements are very indefi- 

 nitely defined. About the margins of the plate the cells possess fairly distinct 

 nuclei and cell boundaries, but in the more central regions bordering the mouth 

 they become distorted, owing apparently to numerous nerve and muscle fibres 

 that either attach to or pass between them to the cuticular plate. 



Darkly staining ductules open to the exterior close to the margins of the 

 plate, and for the first time in my experience have been traced to definite cells. 



