OF THE MAKRAN SERIES. 379 



Subfamily LAQANIN^. 



The Laganidse, as amended by Alex. Agassiz (Rev. Echini, p. 516), were charac- 

 terized by him as follows : — " In this subfamily the connection between the two floors 

 is made by walls running parallel to the edge of the test ; well-developed buccal tubes ; 

 petals lanceolate ; interambulacra extremely narrow on the actinal side of the test ; 

 ambulacral furrows straight, and outline more or less pentagonal." 



Genus LAGANUM, Klein, 1734. 



1. Lagajstum tumidum, Duncan & Sladen. Plate LVIII, Figs. 6-10. 



Marginal contour subpentagonal, with the angles well rounded, or sometimes with 

 a tendency to an oval form. The length is greater than the breadth in the proportion 

 of 1 : 0*957 ; and the greatest breadth is in a line with the termination of the antero- 

 lateral petals. The general form is depressed, but the edges are thick and swollen, 

 forming a broad tumid border to the abactinal surface, between which and the slightly 

 convex central region there is a distinct depression. The tumid border has the 

 appearance of being bevelled towards the margin, and the summit of the test is only 

 very slightly higher than the tumid border. The actinal surface is subplane, or very 

 faintly concave, slightly and abruptly depressed round the peristome. 



The apical system is subcentral and small, having its central area ornamented with 

 small scrobiculated tubercles, and the madreporiform cleft sigmoid or flexuous in out- 

 line. The ocular pores are very small and frequently placed at the side of a small 

 tubercular elevation. The ambulacral petals are long, and extend up to the flank of 

 the tumid border ; they are lanceolate in outline, the zones converging towards the 

 outer extremity, which is almost closed, in fact in some examples may be described as 

 completely so. At the apical extremity the petals appear wide and open. Sometimes 

 the interporiferous area ils faintly inflated, especially near the apical end. The odd 

 anterior petal and the postero-lateral pair are subequal in length, and slightly longer 

 than the antero-lateral pair, and the odd anterior is sometimes slightly narrower than 

 the other petals, but not invariably so. The greatest width of the paired petals is 

 rather nearer the apex than midway between the extremities, and is proportional to 

 the length as 2 : 5, the actual dimensions of the postero-lateral petal in the type 

 specimen being 15 millim. long, and its greatest breadth 6 millim. The poriferous 

 zones are narrow at the apical extremity, but increase rapidly in width as they proceed 

 outwards, and decrease again, but only slightly, along the outer third or fourth of the 

 zone. Both the inner and the outer pores are small and subpyriform, and are united 

 by a distinct but very narrow conjugating furrow ; the intermediate costee are low and 

 comparatively broad, and are ornamented with 2-3 small scrobiculated tubercles and 

 some minute miliary granules forming a serial line ; sometimes the primary tubercles 

 are aborted, and there is then a single line of miliaries. The broadest part of the pori- 

 ferous zone is 1-6 millim., and is more than half the width of the interporiferous area 

 at that place, which is rather nearer the outer end than midway between the extremities. 



