58 FOSSIL ECHINI OF THE WEST INDIES. 



Echinolampas semiorbis Guppy. 

 (Plate 10, Figures 1 to 3.) 



Echinolampas semiorbis Guppy, 1866, Quart. Jour. Geol. Soc. London, vol. 22, p. 299, 

 plate 19, fig. 7. Cotteau, 1875, Kongl. Sven. Vet. Akad. Handl., vol. 13, No. 6, 

 p. 24, plate 5, figs. 1, 2; plate 6, fig. 1; 1897, Bol. Cora. Mapa Geol. Espafia, 

 vol. 22, p. 55, plate 17, figs. 1, 2; plate 18, figs. 1, 2. Lambert, 1915, M6m. Soc. 

 d'Agric. de 1'Aube (Troyes), vol. 79, p. 20. 



The following is an extract from Cotteau 's description of this species: 

 Species of large size, subcircular, a little longer than wide; upper face 

 high, regularly arched, hemispherical; lower face nearly flat, rounded on 

 the borders, subconcave in the middle. Apical disk nearly central, slightly 

 anterior. Ambulacral areas are not elevated, but petaloid, nearly straight, 

 long, widely open at the ends, nearly equal; the posterior pair I and V, 

 however, a little longer than the others. Poriferous areas very well devel- 

 oped, a little depressed, with very unequal pores; the internal pores are 

 rounded, the external long, narrow, and oblique. The poriferous areas 

 in the anterior ambulacra II, III, and IV cease to be petaloid at a con- 

 siderable distance from the ambitus. In the posterior ambulacra I and V, 

 they preserve their petaloid forms a little nearer to the ambitus. Toward 

 the ambitus and lower face the pores become single, very small, widely 

 spaced, and scarcely visible among the tubercles. They reappear and 

 increase around the peristome. Tubercles are strongly scrobiculate, crowded, 

 similar everywhere, abundant, a little more widely spaced at the approach 

 to the mouth. [There are minute granules in the intertubercular spaces 

 on exceptionally well preserved specimens.] Peristome transverse, narrow, 

 subpentagonal, furnished with a floscelle, opening in the middle of the 

 depression of the lower face; a little excentric anteriorly, corresponding 

 in position to the apical disk dorsally. Periproct oval, transverse, infra- 

 marginal. Apical disk compact, prominent, remarkable for the development 

 of the madreporite, which fills the middle of the disk. The two anterior 

 genital pores 2 and 3 are nearer together than are the two posterior pores 1 

 and 4. 



This species is one of the most distinctive of all the species of Echino- 

 lampas occurring fossil in the West Indies. A fine large specimen in the 

 U. S. National Museum (No. 115386), labeled as the type, measures 

 50 mm. in height, 107 mm. in length, and 97 mm. in width. It shows 

 the ornamentation and ventral characters well, but does not show 

 suture lines. Another specimen in the U. S. National Museum (No. 

 115383) is almost an exact duplicate of the above, but is not quite as 

 well preserved, as some plates are wanting; however, it is better in 

 some respects, as the madreporite and characteristic 4 genital pores 

 are clearly preserved and the ornamentation is fine. 



This species, semiorbis, is distinguished from the other West Indian 

 fossil forms by its great size, high dome-shaped test, and flat base. It is 

 very abundant in the island of Anguilla, where Guppy says it is used as a 

 pound weight by the inhabitants. Doctor Vaughan, in collecting at 

 Anguilla, obtained no less than 34 finely preserved specimens, which are 

 strikingly alike in form and even in size. The most obvious difference 

 as a matter of variation is that in some individuals the apical disk is 

 set farther forward than in others, resulting in a more marked posterior 



