592 Verrill, JSFotes on Radiata. 



of Plagionotus {P. pectoraUs and P. Africamis). The two latter 

 species agree in their broad depressed form ; in having the peripetal- 

 ous fasciole convex across the lateral and posterior interambiilacra, or 

 nearly parallel with the margin of the test ; in possessing many very 

 large tubercles, surrounded by a smooth sunken area, bearing large 

 spines, and arranged in oblique transverse rows in all the interambu- 

 lacra, within the fasciole ; and especially in having narrow ambulacra 

 and small ambulacral plates, beyond the petals, while the lateral inter- 

 ambulacral plates are very long transversely and narrow vertically, 

 the latter being six or seven times as long as broad, and five or six 

 times as long as the corresponding ambulacral plates ; and in the 

 anterior interambulacra the plates next the anterior ambulacra are 

 only about half the length of those next the lateral ambulacra, and 

 the latter are much bent, and angulated toward the inner end. 



In Metalia the form is more swollen above ; the peripetalous fasci- 

 ole is curved upward in the lateral and posterior interambulacra, and 

 not at all parallel with the margin ; there are no very large tubercles 

 in the interambulacra, the largest ones, which correspond nearly with 

 the secondary ones of Plagionotus, are chiefly found in the posterior 

 zone and near the anterior ambulacra, in M. noMlis, but they are not 

 arranged in definite rows, and are not at all conspicuous, while in the 

 lateral zones they are very few and scarcely distinct from the small 

 tubercles ; the ambulacra, below the petals, are relatively broad (in 

 M. nohilis about half as wide as the lateral interambulacra), and 

 composed of large plates, while the interambulacra are correspond- 

 ingly narrowed, and composed of fewer plates, which are much broader 

 vertically and shorter transversely than those of Plagionotus / in M. 

 nohilis these are only two or three times longer than broad, and 

 about three times as long as the corresponding ambulacral plates ; in 

 the anterior interambulacra the two rows of plates are nearly equal, 

 and those of both are more regularly curved in the middle. 



In Metalia the ambulacral petals are more sunken than in Plagion- 

 otus, and this is notably the case in 31. nohilis. In the latter and 

 M. Garretii, the vertex is more anterior than is usual in Plagionotus, 

 but this character is somewhat variable. In the character of the 

 lowe* surface the two genera do not materially differ. 



In M. nohilis the actinal area is broadly crescent-shaped, and 

 covered with few, rather large, polygonal plates, which are in close 

 contact. The anal area is also closely covered with angular plates, 

 the outer ones forming a continiious marginal row, in which the lower 

 ones are smallest and oblong or squarish, while the upper ones, filling 



