334 VERRILL 



Ambulacral feet large, flattened, muscular ; can be used as paddles 

 for gliding rapidly along the bottom or just under the surface of 

 sand or mud. 



This family seems eminently worthy of separation from Astropec- 

 tinidae. Its whole structure is adapted to its life under the surface 

 of sand or mud, and for rapid motion. I have observed that Luidia 

 clathrata (see pi. cm, fig. i) swims or paddles with remarkable speed, 

 just under the surface of the sand in shallow water, and that it swims 

 or glides actively in an aquarium, by using its feet as paddles. ( See 

 P. 7-) 



Genus Luidia Forbes. 



Luidia FORBES, Wern. Trans., 1839, p. 14 ; Mem. Wern. Soc., vm, p. 128, 1840. 

 Muller and Troschel, Syst. Aster., p. 77, 1842. Sladen, op. cit, p. 244, 

 1889, Fisher, 191 ib, p. 105. 



Rays five to ten, rather flat, flexible. Dorsal columnar paxillae 

 have lobate, articulated bases; summits either plainly paxillose or 

 with a central spine or tubercle (spinopaxillae), or with both kinds; 

 largest next the lateral borders of the rays. Inferomarginal plates 

 spinose and spinulose. Pedicellariae often absent; when present, 

 forceps-like, with two or three blades or valves. They are usually 

 situated on the adambulacral plates; sometimes on the inferomar- 

 ginals or peractinals. 



Inferomarginal plates transversely elongated, with wide and deep 

 fasciolated grooves between them, bordered by slender spinules; 

 central portion with one or more rows of spines. Superomarginals 

 small, paxilliform, rounded. Adambulacral plates short, with one 

 furrow-spine (rarely two) ; they are separated by wide grooves. 

 The dorsal paxillae may be quadrate at surface and crowded, in 

 regular rows, or stellate. Regular rows of papulae between the rows 

 of paxillae. No superambulacral plates observed. 



LUIDIA FOLIOLATA Grube. 

 Plate c, figures 2, 20; plate cm, figure 2; plate cv, figure 2. 



Luidia fotiolata GRUBE, op. cit., Breslau, XLIII, p. 69, 1866. Fischer, op. cit., 

 19116, p. 106, pi. xix, figs. 1-3; pi. xxi, figs. 3-5; pi. LIV, fig. 3. 



This species grows to large size on the California coast. One 

 from British Columbia has the radii 25 mm. and 205 mm.; ratio, 

 i : 8.2. Another has the radii 18 mm. and 130 mm. ; ratio, 1 : 5.5. 

 The rays are rather flat proximally, gradually tapered to slender tips. 



