DIATOMACEOUS DEPOSIT FROM NORTH TOLSTA, LEWIS. 431 



With respect to the above specimens, of which the measurements have been 

 given, the following remarks may be made : — 



No. 1. The peculiarities of this form have been described above, and are represented in 

 PI. XXIX. fig. 5a. 



No. 2. Striae wider in distal and median inflations than in intervening constrictions. 

 Those in the inflations arcuate and radiate in opposite directions, as in Gomphonema acumin- 

 atum, var. intermedia, Grun. (Van Heurck, op. cit., pi. xxiii. fig. 21), but the external configura- 

 tion of the distal inflation showed that the frustule belonged, not to the variety, but to the 

 species itself. 



No. 3. Striae as in No. 2. From the outline of the distal inflation, which is here much 

 less acute than in the type, though less rounded than in Grunow's var. intermedia, it may be 

 inferred that this was a transitional form between the two, and one which may very probably 

 have its closest affinity with that variety. 



No. 4. Striae somewhat more distant than in the previous forms, especially at the middle 

 of the inflations, but presenting no arcuation, or only the very faintest trace of this, at the 

 distal end, and agreeing more in this respect with the figure given by W. Smith than with 

 that of Van Heurck. Differing from Gomphonema acuminatum, var. coronata ( = Gomphonema 

 coronatum, Ehrenb.), (1) by the less marked distal constriction, and (2) by the character of 

 the distal striation. 



No. 5. Terminal crest, 0*0025 mm. long; its breadth at the base, 00030 mm. Although 

 this frustule is one of the largest observed, its crest has not increased in height, but only 

 slightly in breadth. 



No. 6. Striation in distal inflation similar to that of the corresponding area of Gomphonema 

 acuminatum, Ehrenb., var. intermedia, Grun., but the general form shows that the specimen 

 belonged to the type. 



No. 7. Striation of distal inflation similar to that of Gomphonema acuminatum, Ehrenb., 

 figured by Van Heurck. 



No. 8. Similar to No. 6. 



No. 9. This is the Gomphonema acuminatum, var. coronata of Van Heurck. 



No. 10. Same as No. 9. The number of striae varies considerably in the different parts 

 of the frustules, being fewest in the median inflation and greatest towards the proximal ends. 



No. 11. Typical specimen : distal striae but very faintly radiate. Proximal inflation 

 distinct and proximal extremity more obtuse than in many forms. 



No. 12. Distal constriction more marked that the type figured by Van Heurck ; distal 

 margin of apical inflation more transverse, with straight striae. 



Nos. 13-15. Typical specimens as figured by Van Heurck. 



21. Gomphonema acuminatum, var. coronata, Van Heurck. 

 See supra, Rare. 



22. Gomphonema acuminatum, var. laticeps ? Van Heurck, op. cit., 



pi. xxiii. fig. 17. 



Although approaching this variety, the specimen from the deposit differs 

 from it in the following respects : — (1) The distal constriction is much more 



