334 ROBERT TRACY JACKSON ON ECHINI. 



for, though strictly speaking all have nine sides, some of these sides are very short and almost 

 in a line with one other of those adjoining. The fifth genital (the madreporite) has a width 

 of 3.6 mm. measured at the same level as the other genitals; but, whereas the other genitals 

 scarcely, if at all, increase in width distally, this plate, owing to its greater height, viz., 5.4 mm., 

 attains ultimately a width of 5.7 mm. This plate also is pentagonal in general outline, though 

 it abuts, not only on interambulacrals as do the other genitals, but also on the adjacent ambu- 

 lacra for about 1.5 mm. [I have found so generally in Palaeozoic and later Echini that ocular 

 plates cover the ambulacra and laterally in part the interambulacra on either side (pp. 62, 86) 

 that I think the lack of this latter character in the specimen here described may be due to 

 displacements in fossilization — R. T. J.] 



"Each genital plate, including the madreporite, is pierced by three rounded and well 

 marked pores; but the left anterior has a fourth pore. In three of the four ordinary genitals, 

 these pores follow a curved line, about 0.8 mm. from the adoral margins. In the right posterior 

 genital the two pores next the anterior margin are close together, and one of them is distal 

 to the other. The pores of the madreporite are placed quite differently, one being near the 

 adapical margin, the other two at irregular distances from the adoral margins. It is probable 

 that the normal position of the pores is presented by the two genitals furthest from the madre- 

 porite, and that the modifications in the two abutting on the madreporite were induced by the 

 proximity of the stone-canal, which may have checked the synometrical development of the 

 gonads. [I have not found such irregularity in other cases in this family (Plate 42, fig. 6). — 

 R. T. J.] The genitals are covered entirely but irregularly by miliaries, four or five to the 

 square millimeter. These form circlets round the gonopores. The madreporite also shows a 

 multitude of punctae, much smaller than either the round pores or the miliaries. These may 

 be the usual minute pores of the madreporite ; but they may be due merely to a looser texture 

 in this plate; that is to say, a larger proportion of stroma. On the latter interpretation the 

 pore next the adapical margin, which is larger, more transversely elongate, and in more of a 

 depression than the others, would have been the hydropore, and probably not a gonopore, as 

 all the round pores doubtless were. 



"The periproct is, in the fossil, a pentagonal opening, with a diameter of 4 mm., and almost 

 equal sides formed by the genital plates. The side formed by the right anterior genital (the 

 madreporite) is slightly shorter than the others." 



Of the specimens from Dinant, Belgium, which Fraipont refers to this species, all are 

 moderate sized, with four columns of interambulacral plates in each area, as clearly shown by 

 his excellent photographic figures, which are similar to my Plate 35, figs. 4, 5. He says that 

 the details of the ambulacra could not be ascertained, but, as in every other respect the speci- 

 mens are referable to this species, it seems that they may safely be considered as belonging to 

 L. lacazei. The only other European species in the family which has a spheroidal test and four 



