REVISION OF THE KEYHOLE URCHINS — CLARK 439 



These two bare tests are from La Mancha, Veracruz, Mexico, and are 

 the gift of A. L. Herrera. 



In the Museum of Comparative Zoology there are three specimens 

 of this species, but unfortunately they have no label to show their 

 origin. They have been in the collection for at least 70 years and 

 are labeled MeUita qmnquiesj)erforata and (from early years) Mel- 

 Uta testudinata. The largest is nearly bare but retains a band of the 

 conspicuously capitate primary spines around the posterior margin, 

 dorsally. It is 64 by 74 by 6.5 mm. but is curiously deformed in the 

 anterior left quadrant; petal IV is only 14 mm. long, while II is 

 21 mm., and lunule IV is only 11 mm. long, while II is 14 mm.; 

 there are two genital pores in interambulacrum 2. The second speci- 

 men is smaller 60 by 68 by 7 mm., but is a fine, symmetrical, bare 

 test. The smallest is only 38 by 44 by 4 mm. and still retains its 

 covering of spines, but they are matted together by some sort of 

 adhering and long-since dried slime. Although the origin of these 

 specimens is unknown, they are clearly to be referred to lata and are 

 hence considered paratypes. 



Typical examples of this species are unmistakable, for aside from 

 the excessive width the anterior position of the apex is a striking 

 feature, and the large "heads" of the dorsal primary spines give a 

 texture to the upper surface of well-preserved specimens that is 

 different from the other species of MeUita. 



As yet lata is known only from the eastern coast of Costa Rica 

 and southern Mexico. How far to the north or south it ranges we 

 can only guess, but it apparently does not reach either Texas or 

 Venezuela, as the Mellitas at hand from those coasts are not lata. 

 However, it must be admitted that no Mellitas from southern Texas 

 or western Venezuela are as yet known. 



MELLITA LATIAMBULACRA,= new species 



Plate 62, Figxjbes 3-G 



Descri'ption. — Test moderately thick, 99 mm. long, 106 mm. wide, 

 and 10 mm. high at apex, 40 mm. from the anterior margin, which is 

 2 mm. thick, the posterior margin being little more than half as 

 much. The slope up from anterior margin is rather gradual. 

 Abactinal system very close to apex, but slightly posterior; genital 

 pores four. Petaloid area large, about 60 mm. long by 55 mm. wide ; 

 unpaired petal (from ocular pore to tip) 27 mm. long by 15 mm. 

 wide, narrowed at tip, but not closed; petals II and IV, 28 by 14 mm. 

 a little distal to middle, narrowly open, the interporiferous areas 



* La<MS = broad + ambulacra, in reference to the very wide, oral, ambulaeral, intermediate 

 areas. 



