ANIMALS. 65 
This interesting genus, first noticed by Dr. Scouler, in the ‘ Records of Science’ 
for February 1835, was found by him in a Coal-measure Limestone near Paisley. 
At the meeting of the British Association at Glasgow, Dr. Scouler again described it 
under the name of Argus; but the generic characters have not yet been published in 
full. From the character and contents of the Limestone in which the specimens were 
imbedded, Dr. Scouler considers it probable that the Dithyrocarides found by him 
were the inhabitants of shallow and it may be fresh water.’ 
Two species from the Carboniferous beds have been figured and described by 
Colonel Portlock,’ and two others by Prof. M‘Coy,* from the same formation. On the 
Magnesian Limestone slabs, which furnished the Foraminifera and most of the 
Cytheres above described, there occur many specimens of the carapace-valves of 
Dithyrocaris Permiana, nob. ; the majority, however, are in the condition of casts, more 
or less weather-worn. In the same stratum we have met with a unique specimen of 
D. glypta, nob.; but we have not recognised any of the caudal segments of either 
species. ‘The same difficulty of extracting perfect specimens exists here as in the 
case of the other Microzoa of this rock ; which is the more to be regretted, as certain 
characters of this genus have yet to be distinctly recognised. The relation of the 
valves to each other in the Carboniferous specimens seems constantly to be that 
described by Colonel Portlock,* viz. a horizontal parallelism; but we have found that 
in several instances, especially among the casts, the specimens apparently have their 
valves closed against each other, as in Cythere, instead of being spread out side by 
side, and in contact merely at their dorsal edges. ‘This may be seen from the specimen, 
Tab. XVIII, fig. 1 d, in which one valve has been removed by weathering, and the 
edge of the other valve is apparent around the convexity of the cast. From such a 
cast, but more free from the matrix, the outline, Tab. XVIII, fig. 1 c, was taken, which, 
however, from its worn state, probably does not exactly give the original form. 
Both of the Permian species are much smaller than those from the Carboniferous 
series; and D. Permiana especially differs from the usual type in being nearly bare of 
longitudinal ridges, which circumstance, together with the double-valved character of 
some of the specimens, led me at first to regard it as a Cythere of uncertain sub- 
genus. 
' We are indebted to Dr. Scouler for a courteous communication on the facts connected with 
Dithyrocaris. 
2 Loe. cit. 
* Synopsis Char., &c., p. 163, pl. xxiii. 
* Loc. cit. 
