SYSTEMATIC DESCRIPTION S— CLYPEASTRINA. 37 



Clypeaster dalli (Twitchell). 



(Plate 4, Figure 1.) 



Diplothccanthus ' dalli Twitchell, in Clark and Twitchell, 1915, Monograph U. S. Geol. Survey, 

 vol. 54, p. 218, plate 99, figs. 2a, b; plate 100, figs, la, b. 



The following is an extract from the original description of this species : 

 Test large, pentagonal in outline, longer than broad, widest across the 

 line of ambulacral petals II and IV; pointed anteriorly, posterior end 

 truncated; upper surface irregularly convex, high, highest back of the 

 center, thence sloping in a straight line to the blunt tumid anterior edge, 

 and quite steeply and in a straight line to the thinner wedge-shaped pos- 

 terior edge; the under surface deeply concave. Ambulacral petals large, 

 broad, very tumid, almost reaching to the margin, nearly closing distally; 

 the posterior pair slightly longer than the odd anterior petal, which is 

 slightly longer than the anterior pair. Apical system central, sloping 

 downward anteriorly; 5 genital pores a slight distance from the slightly 

 depressed madreporite. Peristome large, a little excentric posteriorly, 

 subpentagonal, deeply sunken; ambulacral furrows simple, straight, 

 reaching the margin. Periproct rather large, subcircular, inframarginal. 



The specimen in hand, from the Dominican Republic, measures 

 60 mm. in height, 125 mm. in length, and 108 mm. in width across the 

 line of ambulacra II and IV. The height is not far from half the 

 length of the test, the same feature being indicated by Twitchell's 

 measurements of his type material. Clypeaster dalli is a well-marked 

 species on account of its highly swollen petaloid areas, but it is to be 

 remarked that some specimens of C. rosaceus are noticeably swollen. 

 This seems to be just one of those cases in which, among nearly related 

 species, the individual variant of one species takes on the character 

 typical of an allied species. This species was described by Twitchell 

 from the Pliocene, near Fort Thompson, Caloosahatchee River, 

 Florida. The type material, collected by Dr. William H. Dall, is in the 

 U. S. National Museum, No. 164670. 



Miocene or Pliocene, Gato, on the southern side of the island, 

 Dominican Republic, given to Dr. Carlotta J. Maury by the late 

 Senor Rodolfo Cambiarso, of Santo Domingo; Miss Maury very 

 kindly gave it to the National Museum, U. S. Nat. Mus. No. 328234. 



Clypeaster cubensis Cotteau. 



Clypeaster cubensis Cotteau, 1875, Kongl. Sven. Vet. Alcad. Handl., vol. 13, No. 6, p. 6.; 

 1881, Ann. Soc. Geol. de Belgique, vol. 9, p. 16; 1897, Bol. Com. Mapa Geol. 

 Espafia, vol. 22, p. 33, plate 6, figs. 1 to 5. 



This species, of which no material has been available, seems to be 

 valid, as it is remarkably wide in proportion to its length and has very 

 large petals. 



Miocene (?), Matanzas, Cuba, collections of Cotteau in Paris and of 

 Comisi6n del Mapa Ge61ogico de Espafia, in Madrid. 



•Dr. Hubert Lyman Clark (The Genera of Recent Clypeastroids, 1911, Ann. Mag. Nat. 

 Hist., ser. 8, vol. 7, p. 600) does not recognize Duncan's Diplothccanthus as a distinct genus. 



