434 MR JOHN RATTRAY ON A 



side. (2) The constrictions between the extremities and the median portion of 

 the valve are less deep, so that the transition from one part of the valve to 

 another is more easy. (3) The transverse costse are irregular in distribution. 



From Epithemia alpestris, W. Sm. (op. cit., vol. i. pi. i. figs. 7, 7 a, 7b), the 

 frustule figured (PI. XXIX. fig. 7) differs (1) by the presence of fine puncta, 

 disposed in several lines and running across the valve in the intercostal areas ; 

 (2) the ventral margin is much more straight, and the recurvature of the 

 extremities is far less marked ; (3) the disposition of the costae is much more 

 irregular. 



In some specimens, with a more concave ventral side, there is, on both 

 sides of the middle line, a very slight tumidity, extending over a considerable 

 space, and taking away from the curvature considerably. On the entire surface 

 of the valve from sixteen to eighteen costse occur. 



Length of an average specimen, 0*0625 mm.; greatest breadth, 0*0100 mm.; 

 length of recurved obtuse extremities, 0050 mm. 



Not uncommon, and approaching somewhat the Epithemia intermedia of 

 Hilse. 



28. Epithemia hyndmanii, W. Sm. 



Few specimens. These differ from that figured by W. Smith in the follow- 

 ing respects : — (1) The obtusely-rounded extremities are slightly recurved, but 

 much more than is represented by Van Heurck (op. cit., pi. xxxi. figs. 3, 4) ; 

 (2) the outline of the valve on the concave side is uniform, unlike Van 

 Heurck's specimen ; (3) the costation is peculiar, inasmuch as the ribs on the 

 two sides of that which runs partially across the valve in the median transverse 

 line are not symmetrically disposed, but are much more flexed — appearing 

 almost subgeniculate — on one side than on the other. 



Length. 0*1150 mm. ; greatest breadth, 0*0200 mm. ; average distance 

 between the costse, 0*0025 to 0*0028 mm. Intercostal puncta very faint, 10 to 

 12 in 001 mm. 



29. Epithemia sorex, Kiitz. 



Not uncommon. Typical, but more akin to forms figured by Van Heurck 

 (op. (it., pi. xxxii. figs. 6-10) and Kutzing than to those figured by W. Smith 

 {pp. cit., vol. i. pi. i. figs, da, 9b). The two costae bounding the subtriangular 

 central dorsal area are often perfectly straight throughout their length, and it 

 is not without interest to note that in some valves all the costaa are straight. 



Length, 0*0425 mm. ; greatest breadth, 0*0125 mm. ; average distance 

 between the valval costae, 0*0018 to 0*025 mm. 



