VerriU.] 346 



A. Agasslz In tlie Collection of the Essex Institute, fully demonstrates 

 their identity. 



This species has broad, rounded, rather stout rays, which taper 

 rapidly to the obtuse ends, and are somewhat narrowed at the base. 

 Kadii of the disk and arms as 1 : 5. The ambulaeral pores are rela- 

 tively more crowded than in A. arenicola^ though smaller than 

 in that species. The interambulacral plates bear usually two 

 rather long, stout spines, which, as mentioned by Desor, are most- 

 ly obtuse, and canaliculate on the outer side ; toward the ends 

 of the rays, however, they are mostly merely flattened. Outside 

 the interambulacral plates there is a row of small, thick plates, 

 with wide spaces between. These plates often, though not always, 

 bear each a short spine, forming a row that fades out towards the ends 

 of the rays. External to these is a crowded row of prominent, ob- 

 lique, stout plates (ventrals), each of which bears usually two, or 

 sometimes three, spines on its oblique prominent portion, and one on 

 a rounded external tubercle alternating with them, thus forming throe 

 or four irregular rows of thick, obtuse spines. These are separated 

 from the "laterals" by a well marked, broad space, having large open- 

 ings between the plates, which become much wider toward the base 

 of the rays, causing the lateral rows to curve rapidly upward toward 

 the dorsal area of the disk. The lateral plates are strong and closely 

 imbricated, bearing two or three principal spines, often with other 

 smaller ones between, forming several closely crowded, irregular rows. 

 External to these, the dorsal area of the rays is covered with rather 

 numerous, short, blunt spines, not arranged in very distinct rows, but 

 a median row is often pretty well marked, though scarcely longer 

 than the others. On the disk the spines are more crowded. The 

 lateral spines are longer than the dorsal, and the ventrals still longer 

 and stouter. The principal dorsal and lateral spines bear crowded 

 wreaths of minute, short, obtuse, minor pedicellari£e. Clusters of 

 larger pedicellarise are found on the outer surface of the ventral and 

 interambulacral spines. They are also numerously scattered on 

 the surface between the spines. These are short and stout, broad 

 oval, obtuse at the tip. The texture of this is much firmer than that 

 of the following species, owing to the stouter and more numerous 

 plates, especially on the dorsal area. Specimens prepared by soaking 

 in caustic potash, until the soft parts are removed, show this differ- 

 ence very distinctly. The madreporic plate is prominently convex. 



A dry specimen, of ordinary size, is 2.9 inches from the centre of 

 the disk to the end of the rays; 0.6 inch to edge of disk ; greatest 

 width of rays 1 inch; length of interambulacral spines .13; diameter 

 of madreporic plate .18. This species occurs at the South Shoals, 

 (Desor), and is abundant along the eastern coast of Massachusetts, 



