16 Vrof. P. Martin Duncan — On Galerites alhogalerus, Lamh. 



fallacious as that regarding the teeth. On cleaning out a good 

 specimen which was filled with chalk no trace of auricles could be 

 found, and the so-called " casts " are extremely rudimentary. The 

 interambulacra thicken close to the peristome, and between the 

 rounded thickening and the edge of the peristome is a depression, 

 and it is this which, in the state of cast, simulates the auricular base. 

 But it is really not in the position of such a base. 



Galerites alhogalerus is then edentulous, and has no auricles. 

 The position of the periproct (anus) is not altogether infra-marginal 

 in perfect specimens. Its upper part can be seen on the margin 

 when the test is looked at from behind on a level with the eye. 



The apical system most certainly does not show a fifth genital 

 plate. About 40 of the specimens examined by me show the apical 

 details very well. There is some variability of the arrangement of 

 the postero-lateral genital plates, and the posterior oculars, but I 

 have never seen the madreporic body which, as usual, occupies an 

 enlarged right anterior genital plate pass backwards and separate 

 the posterior oculars. The disk is very compact, and the following 

 are the variations in the relations of the plates. 



1. The madreporic plate reaches over the median line, is in 

 contact anteriorly with the much smaller left anterior genital plate, 

 and with the odd anterior ocular. The madreporic is in contact 

 posteriorly with the postero-lateral genital plates and the right 

 posterior ocular plate. The right antero-lateral ocular plate touches 

 the madreporic, and the left antero-lateral ocular is occluded by the 

 junction of the left lateral genital plates. The left posterior ocular 

 plate is not in contact with the madreporic. 



2. The same — but the left antero-lateral ocular plate separates the 

 left lateral genital plates, and comes in contact with the madreporic 

 plate. 



3. The same — but both posterior ocular plates, which are small, 

 are in contact with the madreporic (Brit. Mus. 38,723, and 38,731). 



4. The postero-lateral generative plates unite along the median 

 line and separate the madreporic from the posterior oculars (Brit. 

 Mus. 38,731, middle specimen on the tablet). 



5. The postero-lateral generative plates unite to the left of the 

 median line. 



The occasional entry of the right posterior ocular plate into the 

 ring is accompanied by its increase in size, and by the pushing 

 backwards and to the left of the left ocular plate. Loven's (plate 

 XV. fig. 134, Etudes) delineation represents one of the commonest 

 of the above variations. The drawing of the apical disk by Desor, 

 Forbes, and Wright is absolutely wrong. Cotteau and Triger show 

 a rare variation, but I have never seen the small genital plate they 

 represent. 



The ambulacra, above the margin of the test, are not equal and 

 rectangular as drawn by Forbes and Wright. At a short distance 

 from the ocular plate, and where the breadth of the ambulacre cor- 

 responds with that of the drawings of the above-mentioned authors, 

 the plates in succession are unequal, and one does not reach the 



