252 Prof. P. M. Duncan on the Salenidge. 



plate is forwards and to the right ; and I am impressed with 

 the truth of the observations and demonstrations of the great 

 Scandinavian naturaUst relating to the distribution of the 

 pores and tubercles at the peristoniial margin with reference 

 .to the antero-posterior axis of the test. A. Agassiz main- 

 tains the exactly opposite opinion, and places the madre- 

 poric plate posteriorly and to the left. As the question has 

 been ably advocated by the above-mentioned authors, it is 

 only necessary to refer to their works on the subject. But it is 

 by no means easy to distinguish the madreporic plate from the 

 others in most Salenida ; yet a guide to its position may be 

 found in the fact that the anus proper infringes upon two 

 generative plates, which in the genus Salenia are posterior, 

 or rather one is posterior and the other posterior and to the 

 right ; hence the madreporic plate will be found immediately 

 anterior to this last-mentioned plate. If the test be so placed 

 that the generative plates are in this position, an ocular plate 

 (that to the left of the madreporic plate) will be directly ante- 

 rior, and a line drawn through its middle and carried directly 

 backwards will run along the suture between the madreporic 

 plate and the left anterior generative plate, and will pass over 

 the so-called sub- or suranal plate and reach the margin of 

 the anus. 



In the new species of Salenia the abactinal system, more 

 or less pentagonal, covers nearly the whole of the abactinal 

 surface : it is irregularly convex, and the highest point is not 

 quite central, and is situate in a part of the raised margin of 

 the eccentric anal orifice where it is in contact with the sub- 

 anal plate (subanal meaning before the anus) (fig. 8). This con- 

 vexity, accompanied as it is by an eccentric position of the 

 anus, which, moreover, slopes backwards and to the right, 

 renders any delineation of the apical disk, except as a diagram, 

 very incomprehensible. The subanal plate is central, the anal 

 opening infringing on its posterior and right part ; and it 

 slopes away from the raised margin of this opening. The pos- 

 terior and the right posterior generative plates, which with 

 the subanal plate contribute to the anal opening, are narrow, 

 the orifice reaching not very far from their outer edges. To 

 complicate the comprehension of the disk, the whole surface is 

 studded with papillas, — not embryonic spines ; for they are not 

 placed on tubercles, but are ininute wart-like projections of the 

 test, usually smallest at the base and rounded at the top, the 

 whole surface being reticulate, mulberry-looking, and pigmented 

 with dark-violet grains in the furrows (fig. 3). Some are 

 thin, and some are longer than others ; some, especially in the 

 margin of the anus, are broad ; and many are crowded in the 



