496 PROFESSOR GREGORY ON 



that D. minor almost looks like a miniature of D. distans ; but on a close compa- 

 rison, they are found to be totally distinct. D. distans often occurs shorter than 

 the average length of D. minor, but it never loses its own characters, the strong, 

 distant, glassy costse, and the broad S.V. But the two forms are evidently allied 

 species, and both seem to be true Denticula. 



37. Dentimla staurophora, n. sp. PI. X., figs. 37, 37 b, and 37 c. Form of 

 F.V., which occurs in chains of two, three, and sometimes more, rectangular, with 

 coarse marginal striae, which in the middle on each side, are interrupted by a 

 blank space, bounded by diverging lines. Length from 0001" to 0*0038" ; breadth 

 0-0005" to 0-0008", the shorter examples being the broadest. S.V. lanceolate, rather 

 narrow, marked with coarse moniliform strise, except in the middle, where there 

 is a broad stauros, on each side of which is a line, curved and concave towards 

 the extremities. Strise 14 to 16 in 0001". 



This striking form is not unfrequent either in Lamlash Bay or in Loch Fine. 

 I have referred it to Denticula, but perhaps it ought to be referred to Diadesmis, 

 or, if the stauros be considered an objection, to a new genus allied to Diadesmis 

 as Stauroneis is to Navicula. But this point must be left for farther investi- 

 gation. 



38. Denticula fidva, n. sp. PI. X., figs. 38 and 38 b. Form of F. V., which oc- 

 curs in chains of two, three, and sometimes four, linear, rectangular, and slightly 

 expanded at the apices, the margin marked with the ends of somewhat coarse 

 strise. Length from 00018'' to 0004'; breadth 00005". S.V. linear, narrow, 

 broadest in the middle, and gradually contracting to long, narrow extremities, 

 which are ultimately subcapitate and rounded. Striae moniliform, somewhat 

 coarse, leaving a raphe in the middle, and the two terminal knobs unstriated. 

 No central nodule in the S.V. ; but the two nodules seen at each end of the F.V. 

 appear to form the unstriated knobs at each end of the S.V. 



This well-marked species occurs with the three last, and is even more fre- 

 quent than they are. The genus cannot be considered as determined with cer- 

 tainty. 



39. Denticula marina, n. sp. PI. X., figs. 39 and 39 b. Form of F.V. linear, 

 rectangular, with the angles very slightly expanded, and the margin strongly 

 denticulate. It occurs in chains of from 2 to 18 or 20, so that the filament 

 seems to be tenacious. Length from 0002", to 0*008" or 0*009" ; breadth from 

 0*0003" to 0*0005 ". S.V. linear, expanded at the middle, and obtusely acuminate 

 at the ends . Striae very coarse, and very coarsely moniliform, about 10 in 0*001". 

 On each side of the median line each of the strise is formed of only two granules, 

 which are distant, and half of a third, which seems to be on the margin. The two 

 or three central strise on each side, having only one and a half granules, the inner 

 granule of each being absent, there is a blank space round the centre ; and there 

 is a smaller blank at each apex. The F.V. here figured is of about the usual 



