1835.] which occur in the Coal formation. 137 



on splitting up the rock we observe impressions of ferns 

 of great rarity and beauty, the remains of entomostraca 

 which are of gigantic size, when compared with the ana- 

 logous species which still abound in our lakes and pools. 

 Two species belonging to a new genus were obtained, and 

 the number might have been greatly increased, had not the 

 hardness of the rock rendered the extraction of the speci- 

 mens a difficult task. The following is a short description 

 of these remains : 



1 . Argas testudineus, (Fig. 1 .) The shell is rounded and 

 deeply emarginate at its anterior extremity, and surrounded 

 by a thinner margin ; the epidermis is covered with nu- 

 merous elevated lines. Two ridges extend through the 

 whole length of the shell, one on each side, their position 

 being intermediate between the margin and the middle 

 line. The tail (abdomen) is articulated, but the number 

 of joints is uncertain, perhaps seven or eight, and it termi- 

 nates in three appendices (respiratory organs ?) as is the 

 case in the recent genus Apus. In our specimen these 

 appendices are of equal length, and have a similar form, 

 while in the genus Apus, the middle one is the shortest, 

 and its form is different from that of the others. No ves- 

 tiges of eyes, antennae or organs of locomotion could be 

 observed. The length of the specimen from the anterior 

 margin of the shell to the extremity of the tail is 2$ inches. 

 Length of the shell li inch. Breadth V 5 inch. The shell 

 has a considerable resemblance both in size and form to 

 the dorsal shell of some of the fresh water turtles, and 

 hence the appellation, which we have ventured to give to 

 the species. 



2. Argas tricornis, (Fig. 2.) The shell is elliptical but 

 truncated anteriorly, and much more depressed than in the 

 preceding species, and a single ridge runs in the direction 

 of the middle line. At the anterior extremity of the shell 

 there are three acute triangular processes, one at each 

 angle of the shell and one in the middle. Two grooved 

 lines extend around the circumference of the shell," the one 

 internal, separating the margin or thin portion from the 

 rest of the shell, and the other line external, dividing the 

 margin into two distinct parts. The posterior extremity of 

 the shell is very indistinct, and the number of joints in the 



