from the Fossiliferous Limestone of Durham. 433 



scription given by M'Coy is very short, and his figures represent 

 only a portion of a carapace : the former would apply to many 

 species besides the one to which it refers, so that it is not of 

 much use in the determination of apparent affinities ; but his 

 figures show that the Carboniferous species had at least one 

 prominent rostrated extremity, and that it was compressed and 

 concave laterally towards the extremities, — characters which 

 certainly distinguish it specifically from its supposed Permian 

 representative. 



Most of the specimens of this species which have occurred at 

 Tunstall Hill are coated with a thin deposit of calcareous matter; 

 and it is not until this is removed that their relation to Bairdia 

 can be detected. 



It is not rare in the fossiliferous limestone of Tunstall Hill. 

 In Germany it is found in the Lower Zechstein of Bleichenbach, 

 Selters, and Saalfeld. 



B. Jonesiana is named after Mr. T. Rupert Jones, to whom I 

 am indebted for several courteous communications on Permian 

 Entomostraca. 



Bairdia truncata, n. sp. PI. XI. figs. 4 & 4 a. 



Length ^V mcn i beight fa inch. 



Carapace subrhomboidal, inflated ventrally in anterior half, 

 smooth (?) . Dorsal margin almost straight, though slightly 

 convex; anterior slope gradual, convex; posterior slope very 

 abrupt, descending nearly the whole of the height, convex. 

 Ventral margin rather convex, with a short projection near the 

 anterior extremity. Anterior extremity rounded, prominent. 

 Posterior extremity diagonally truncate. Lateral contour irregu- 

 larly lenticular ; greatest diameter in anterior half two-sevenths 

 of the length, pointed anteriorly, bluntly rounded posteriorly, 

 sinuate in posterior half. 



The few specimens of this species which I have found are casts ; 

 consequently the above description is probably incomplete and 

 subject to modification. That it belongs to Bairdia is evident 

 by traces of an overlapping of the dorsal margin. Its marked 

 difference from all the Permian species which have preceded it 

 has induced me to describe it as a species, though from imperfect 

 materials. 



Rare in the fossiliferous limestone of Tunstall Hill. 



Bairdia rhomboidea, n. sp. PI. XI. figs. 3 & 3 a. 



Length fa inch ; height fa inch. 



Carapace subrhomboidal, protuberant centrally, smooth. Dor- 

 sal margin prominently convex, sloping gradually to each extre- 

 mity. Ventral margin very convex, more so anteriorly than 



