518 LAGANUM DEPRESSUM. 



Laganum elepressuni 



! Layanum deprosoum Less., 1841, i-i Ac. vs.-, Mon. Scut. p. 110. 



PI. XIIF.f. 6-8 ; PI XXX III./. .;, 4. 



The synonymy of this species shows its great range of variation. The 

 test is more flattened than in L. Bonani ; the edge thinner, not swollen ; the 

 posterior extremity more angular. The anus is nearer the posterior edge, 

 and is transversely elliptical, or circular ; the apical system is larger. 

 The tuberculation small and crowded on the abactinal side ; on the actinal 

 side the tubercles are larger, more distant, especially in the slightly depressed 

 interambulacral spaces, where they are so far apart as to form fan-shaped 

 areas, extending from the aetinostome to the edge, where the tubercles are 

 more distant than in the adjoining portion of the actinal surface. The am- 

 bulacra! furrow-; are broad, extending nearly to the edge of the test. The 

 peristomal star is distinct, while in L. Bonani it cannot be traced in any 

 specimen I have examined. The spines of the abactinal and actinal sides 

 are similar to those of the actinal side, longer, more slender, and more dis- 

 tinctly fluted ; seen from the interior, the concentric walls of the edge of 

 the test occupy a relatively broader space, and me more numerous than in 

 L. Bonani. The jaws are powerful, high ; the two ] osterior jaws much larger 

 than the anterior ones ; the odd jaw far the smallest. The petals in small 

 specimens of 27""" in longitudinal diameter extend much nearer the edge 

 than in L. Bonani : in older specimens measuring ( L. Tonganense) To""" . 

 longitudinal diameter, the outline become- more angular, with re-entering 

 sides. The petals extend but a short distance beyond hall-way between the 

 apex and the edge Oi the test. In these large specimens the anus becomes 

 more circular. In alcohol the color is of a dirty yellow. 



The greatest transverse diameter is placed behind the anterior pair of 

 ambulacra in old specimens, while it is directly across the tip of the same 

 in smaller specimens; the difference between .the longitudinal and transverse 

 diameter becoming less with diminishing size. 



The pairs of pores are more separated as they near the tip of the petals, 

 where they are quite distant, though nowhere in the poriferous zone are 

 they as indistinctly conjugated ;is in L. Bonani ; the grooves connecting 

 them become obliterated with age. A fine series of this species, collected 

 at New Caledonia, in the possession of Mr. Crosse, has enabled me to solve 

 many doubtful points regarding the synonymy of this species. 



