REVISION OF THE KEYHOLE URCHINS^ — CLARK 443 



The color is uniformly brown ; orally the test is a brighter, more 

 yellowish, brown than on the upper surface. 



Locality. — Northwest of lighthouse 2 miles outside of Sanibel 

 Island, Fla., from a sandbar in 3-4 feet of water; W. J. Clench, 

 February 1929. 



Eolotype.—V.S.'^.ISL No. E.5656. 



Notes. — There are in the United States National Museum two para- 

 types of this variety. The larger is from Tarpon Springs, Fla., 

 where it was collected by Edwin J. Shadle. It is 98 by 102 mm. in 

 diameter and is a lighter and yellow^er brown than the holotype. 

 The other specimen, collected by Dr. W. H. Dall at Charlotte Harbor, 

 Fla., is almost circular, 55 m. in diameter, and has the apex unusually 

 far back, just in front of the unpaired lunule. The color is like the 

 Tarpon Springs material. In the Museum of Comparative Zoology 

 collection are a number of specimens of this variety from Sanibel 

 Island, Fla., of which half a dozen are paratypes collected with the 

 holotype by Mr. Clench in February 1929. The smallest is only 

 4i mm. long and almost 44 mm. wide; the test is very thin and 

 delicate, scarcely 3 mm. thick at the apex, which is very close to the 

 center of the test; the color is a deep gray above, light brown 

 beneath, with many light greenish-blue lines and areas, specially near 

 the mouth. The larger specimens are like the holotype in color 

 and range from 74 to 104 mm. in length, with the width the same 

 or a millimeter more or less, except one that is 99 mm. long by 

 104 mm. wide. In all these specimens the apex of the test is at or 

 behind the center, and the lunules are uniformly small. Besides 

 these specimens the Museum of Comparative Zoology contains, also 

 from Sanibel Island, a bare but not bleached test 120 by 125 mm., 

 a water-worn test 78 by 81 mm., and a very young specimen only 

 19 mm. in diameter in which the paired lunules are not yet closed 

 in. There are also five small specimens from an unknown locality 

 of which the largest is 71 by 68 mm., with the apex very evidently 

 at the anterior end of the unpaired lunule, while the other speci- 

 mens, 48-57 mm. long (with width about the same), are rounded 

 pentagonal, more or less asymmetrical, and have the anterior margin 

 notably straight rather than curved. There are also 10 very young 

 Mellitas, 23-36 mm. in diameter, dredged half a mile off the eastern 

 end of Sanibel Island in 1-2.5 fathoms by W. J. Clench on 

 April 6, 1933, which are naturally to be considered the young of 

 tenuis, although of course in such immature specimens the varietal 

 characters are not conspicuous. But the posterior position of the 

 apex is a fairly distinctive feature. The Museum of Comparative 

 Zoology has also a paratype from Tarpon Springs, Fla., taken by 

 Edwin J. Shadle, 89-93 mm. in diameter, received from the United 



