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 

 Bithyrocaris 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 I). 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. 

 ^ Loc. cit. 



•* Synopsis Char., &c., p. 163, pi. xxiii. 

 * Loc. cit. 



