LAGANUM DEPRESSUM. 45 



Key to the Species of Laganum. 



Genital pores at proximal ends of interambulacra, more or less eloso to madreporite. 



Anus midway between margin and mouth, longitudinally elongated; test thick, with 



depressed pet aloid area and swollen margins laganum. 



Anus distinctly nearer to margin than to mouth, usually transversely elongated; test 

 with petaloid area more or less elevated and margins not swollen. 

 Petaloid area relatively large, its total length .60 test-length or more; test with 

 more or less pentagonal ambitus, its length usually decidedly greater than 



breadth depressum. 



Petaloid area relatively small, its total length ..50 test-length or less; test with 

 decagonal or rounded ambitus, its length little, or not at all, exceeding 

 breadth. 

 Petals small but relatively broad, with curved poriferous areas, converging 



to the nearly or quite closed tip; test low, v. d. .13-.18 test-length decagonale. 

 Petals narrow, poriferous areas little curved and tips widely open. 



Test relatively high, v.d. ranging from .20 to .40 test-length; posterior 

 interradius with one genital pore; tuberculation of test rather coarse 

 (within a petal 10 mm. long there are about 20-25 primary tubercles 



and in one 15 mm. long, there are about 40-50) judsiyama. 



Test lower, v.d. less than .20 test -length; two genital pores generally 

 present in posterior interradius; tuberculation of test finer (within a 

 petal 10 mm. long, there are 40-50 primary tubercles and in one 15 



mm. long, there are 80-90) diploporum 



Genital pores in interambulacra, some distance from madreporite putnami 



Laganum laganum. 



Echinodiscus laganum Leske, 1778. Add. ad Klein, p. 140. 

 Lagana laganum de Blainville, 1830. Diet. Sci. Nat., 60, p. 196. 



Plate 124, fig. 17. 



The tridentate pedicellariae of this species are rather characteristic and as 

 they have never been figured, I have thought it desirable to show one valve 

 (PI. 124, fig. 17). The geographical range of L. laganum is from the Philippine 

 Islands, east to the Carolines, and southward to Tasmania. 



Laganum depressum. 



Agassiz, 1841. Mon. Scut., p. 110. 



Plate 124, figs. 7-12. 



So far as I can judge from his description, the Laganum, which Mazzetti 

 (1895, Mem. Reg. Accad. Sci. Modena, ser. 2, 10, p. 217) described as new 

 under the name fragile , is simply one of this species. 



