498 PROFESSOR GREGORY ON 



lations. S.V. linear, narrow, broadest at a point above the middle, from which it 

 becomes narrower both ways; the shorter half being rather broader than the other, 

 and rounded at the apex. The longer and narrower half is also rounded, and 

 very slightly expanded at the end. Striae coarse, not reaching the median line, 

 but leaving a somewhat broad raphe in the middle. Strise about 16 in 0001" ; 

 Length about 00015"; breadth of F.V., at larger end, 0-0004", at smaller end. 

 00003". Breadth of S.V. 00002" at the broadest point. 



This form resembles both a Meridion and a Gomphonema. The absence of a 

 central nodule prevents me from referring it to the latter genus ; and with reference 

 to the former, the mode of attachment, as well as the form of the frustules, agree 

 pretty well with it. But I have not seen more than four attached ; so that it is 

 still doubtful whether it forms a spiral filament, as the slightly cuneate frustules 

 must tend to do. It occurs, by no means sparingly, both in Lamlash Bay and in 

 Loch Fine. Future observations on the living form will decide the question of 

 its generic position, but in the meantime it is a well-marked species. 



42. Pyxidicula cruciata, Ehr. PI. X., fig. 42. Form of V. cup-shaped, hemi- 

 spherical, with hexagonal cells over the whole surface, and in one direction, a 

 crest composed of square or irregular cells running round the hemisphere in a 

 plane at right angles to that of the junction of the two valves. Cells large, and 

 of uniform size. Diameter 0*0019". 



The form here figured is only a detached valve, the entire frustule not having 

 yet occurred in these dredgings. But it agrees precisely with Ehrenberg's figure 

 of the valve. The specific name is given on account of the arrangement of some 

 of the cells, as seen in a view obtained by looking down on the frustule, at right 

 angles to the junction, in the form of a broad rectangular cross. This cannot be 

 seen in the view here figured. The species is very scarce as yet, having occurred 

 very sparingly in Lamlash Bay. But it is interesting, as being one of the forms 

 which Ehrenberg has figured from the yEgina Clay Marl already mentioned at 

 p. 482, and from the deposit of Richmond, Virginia. I have placed it in this 

 group, because I have reason to think that Pyxidicula is a catenate form, 

 though we cannot expect to see this in fossil deposits. I would here refer to 

 the beautiful new form, detected by Professor Walker Arnott, and figured in 

 the Appendix to this paper, which, in the frustules, is so closely allied to the 

 present species, that it may prove to be actually P. appendiculate of Ehrenberg, 

 a form which occurs along with P. cruciata. Professor W. Arnott's form is 

 decidedly catenate. \ 



43. Orthosira angulata, n. sp. PL X., figs. 43 and 43 b. Form of F.V., which 

 occurs solitary, and in chains of from two to six, rectangular in the middle, acu- 

 minate and truncate at the ends. On the margin, which is often slightly incurved, 

 are seen denticulations arising from the cells of the disc or S.V. Length from 

 0-0005" to 0-0015" ; breadth of F.V. from 0-0003" to 000045". Diameter of disc, 



