Paleozoic Bivalved Entomostraca. 333 
Our fellow-workers in North America also have contributed 
to the geological history of these Ostracodes. 
The gradual accumulation of specimens, and an improved 
acquaintance with their special characters, have enabled my 
colleagues, Dr. Holl, Mr. Kirkby, and Prof. Dr. G.S. Brady, 
and myself to offer at times some remarks on Paleozoic and 
other fossil bivalved Entomostraca; but, excepting as to the 
Carboniferous Leperditia Okeni and its varieties and allies, 
we have had little certain information to add to the general 
stock about this genus in particular. I have now, however, 
put together some notes and sketches illustrative of various 
doubtful points in the alliance of some British and other 
Leperditic, endeavouring to improve, if not simplify, their 
nomenclature. At the same time I have to introduce a few 
species not previously recognized. 
In 1869 Dr. Lars Kolmodin * indicated the difference of 
form between certain specimens figured in the Ann. & Mag. 
Nat. Hist. 1856 (namely, pl. vi. figs. 1, 2, 4, and 5, on one 
hand, and fig. 3, a-e, on the other) as giving a varietal dis- 
tinction ; and in 1873 Fr. Schmidtt established a new species 
for Kolmodin’s “var..6”’ (fig. 3, a-e, above mentioned) with 
the name of L. Hisingert, illustrating also two varietal forms 
by his figs. 22 and 23. Subsequently | Dr. Kolmodin ob- 
jected to this name, under an erroneous impression that it was 
the same as ‘Cytherina Hisingert” § as applied by Minster, 
and he substituted “LZ. Schmedti.” 
There are certain differences between the more oblong cara- 
paces of L. balthica (I. c. figs. 1, 2, 4, 5) and the more ovate 
form (fig. 3, a—e), as to both outline and relative convexity, 
the oblong form having the longest hinge-line, and being 
thickest at the anterior third, the other having a shorter 
hinge-line and being most convex in the middle. 
In my paper of February 1856 (p. 86) I referred these dis- 
tinctions to difference in age. ‘The oblong form is rare. 
Large individuals are by no means common, I believe; and 
I have seen only one rather small specimen having this shape 
(in the British Museum), besides the two small valves shown 
by our figs. 10 and 11, and the imperfect valve shown by 
fic. 1 of our Plate XIX., which probably belongs to the form 
* ‘Sveriges Siluriska Ostracoder,’ p. 14, figs. 4 and 5. 
+ Russ. silur. Leperd. p. 16. 
} “Ostracod. Silur. Gotland.” 1880; Cifv. K. Vet.-Akad. Forh. 1879, 
p. 133. 
§ See Ann. & Mag. Nat. Hist. ser. 3, vol. xv. p. 408, pl. xx. figs. 12, 
a-c, where Jones and Kirkby defined Count Munster’s Carboniferous 
species. 
