On a fossil Crustaceous Animal. 377 



From the preceding description and accompanying plate, 

 which is of the natural size, it is evident that this fossil must 

 be referred to the order of branchiopodal Crustacea. In the 

 form and structure of the eyes, it resembles the lsotelus de- 

 scribed in the preceding volume of the Annals, which was 

 referred to the family of Trilobites, and yet the presence of 

 natatory feet, branchial filaments, and more especially the 

 absence of longitudinal lolies, would separate it decidedly 

 from that family. It would be very desirable to ascertain its 

 proper place in the natural series, and to determine whether it 

 might not form a connecting link between the groupe of Tri- 

 lobites, and some recent genera of the branchiopodal Crustacea. 

 A cursory inspection of its external form would lead us at 

 first to place it among the decapodal order of the family Mac- 

 rouri The character of that family however will not permit 

 this and a minute examination of the order Branchiopoda. 

 Lat. Eutomostraca of others has also failed to satisfy us in 

 this respect. We may be permitted to indicate Apus, Binocu- 

 lus, and Lepidurus, as the genera to which the present relic 

 seems nearest allied. 



We can offer little of interest respecting its geological 

 situation, as it is not known whether it was found in place, 

 or in a detached mass. From the weathered appearance 

 presented by one of its surfaces, we should be inclined to 

 adopt the latter opinion. The rock containing the impres- 

 sion is, as far as we are acquainted, peculiar to this country. 

 It is termed by the country people, bastard limestone, and 

 has had the usual fortune of most of our rocks, to have been 

 described under many different names. It is said to be clay 

 slate by Dr. Mitchill ; grey wacke slate, calciferous sand 

 rock, transition sand rock. &ic by others. It is of a bluish 

 color, with a conchoidal fracture, homogenous appearance 

 and earthy smell. It effervesces slightly with acids, con- 

 tains a few siliceous partifl^s. nnd srives (ire with stcc]. 



