306 VERRILL 



The adambulacral spines, which are usually two to a plate, inner 

 and outer, increase in length and become terete, instead of flat, at 

 the tips of the arms, while some of the distal interactinal and inferior 

 marginal plates sometimes bear short, thick, stumpy spines, especially 

 in large specimens. 



In formalin preparations the entire surface is covered with a 

 thick, soft skin, deep brown or yellowish brown in color, which 

 entirely conceals the ossicles and spines (pi. xxix, fig. 2), but the 

 groups of papulae on the back are quite distinct. In life this skin is 

 very soft and covered with abundant mucus. In some dried prepa- 

 rations the integument is like a sort of thin varnish over the surface, 

 leaving the ossicles easily visible, but in other cases it is so dried 

 that the ossicles are mostly concealed. The principal dorsal ossicles, 

 both on the rays and on the disk, have a regular stellate arrangement, 

 as stated by Agassiz. Each large ossicle is roundish, with slight 

 lobes, connected with five to eight small, radiating connective 

 ossicles. In the interradial regions the ossicles are stouter, are not 

 stellate, and are closely imbricated. In this area there are few or no 

 papulae. The interactinal plates are broad ovate, and form rows 

 parallel to the ambulacra. They are distinctly altematingly imbri- 

 cated, like slates on a roof. Papulae are very numerous and form 

 large groups on the dorsal side of large specimens, but stand singly 

 on young ones. 



There is an incomplete, partly calcified interradial septum, extend- 

 ing outward from the jaws, composed of rather large rounded 

 ossicles. Superambulacral plates ( ?) of small size are present. For 

 some details of the skeleton see pi. lxxxvi, figs. 2-2d. 



Only one species of the genus is known. 



DERMASTERIAS IMBRICATA (Grube) Perrier. 



Plate VI, figures 3. 4, 5; plate xxix, figure 2; plate L, figures 1-1& (pedicel- 

 lariae) ; plate lxxxvi, figures 2-2d (skeleton) ; plate xcvii, figures 2-2b 

 (variety). 



Asteropsis imbricata Grube, Wieg. .^rchiv, xxiii, p. 340, 1857. Verrill, Trans. 

 Conn. Acad. Sci., i, p. 324, 1867 (distribution). A. Agassiz, North Ameri- 

 can Starfishes, p. 106, pi. xv, figs. 1-7, 1877 (structure). 



Dermasterias inermis Perkier, Revision Stellerides, p. 282, 1875. 



Dermastcrias imbricata Perrier, Arch, de Zool. Exper., v, p. 98, 1876. Viguier, 

 op. cit., VII, p. 218, 1878. Sladen Voy. Chall., xxx, p. 766, 1889. Whiteaves, 

 Trans. Royal Soc. Canada, iv, p. 117, 1887. Clark, Proc. Boston Soc. 

 Nat. Hist., XXIX, p. 325, pi. i, figs, i, 2, 1901. Fisher, op. cit., igiib, 

 p. 249, pi. XL, figs. I, 2; pi. LVI, fig. I. 



