CONTRIBUTIONS TO PALAEONTOLOGY. 181 



GENUS AGLASPIS ( n. g.). 



The investigations in the upper part of the Lower sandstone of 

 the Mississippi valley have furnished me with the carapace, some 

 fragments of the thoracic articulations, and what appears to be a 

 caudal spine of a new and remarkable crustacean, for which I 

 have proposed the name Aglaspis.* 



Generic description. Carapace wide, sublunate, or approaching se- 

 micircular ; its superior crust not separable into parts by suture 

 lines ; a sinus in the middle of the front, and preserving some 

 evidence of trilobation in the posterior part. Eyes anterior to 

 the middle, large and prominent. 



Thorax probably subtrilobate, composed of several articulations, 

 which are recurved at their extremities. Posterior or caudal 

 portion more elevated in the middle and strongly arching : the 

 caudal extremity probably furnished with an elongate spine. 

 Texture punctate. 



The only species known, in its carapace reminds one of Limulus ; and 

 though the resemblance is not so apparent in the character of the eyes, yet 

 we find that these organs occupy the relative position of the two oculiform 

 spots on the anterior part of the carapace of that animal. The segments of 

 the abdomen, which in that genus are anchylosed, are here free, in their 

 anterior members at least ; while the posterior ones are highly arched and 

 closely united. The associated spines, of the same texture as the other parts, 

 can scarcely have had any other relation to the body than the caudal spine 

 of Limulus ; and the Aglaspis, with its broad depressed-convex cara- 

 pace and its anterior eyes, was furnished with a long caudal spine as in 

 the modern genus. 



AGLASPIS BARRANDI ( n. s.). 



PLATE XI. FIGS. 7 - 16. 



Carapace sublunate or semicircular, the diameter at base being 

 more than twice the length ; sides moderately convex ; the 

 middle more elevated, and showing indications of a trilobate 

 character : front emarginate, or with a distinct sinus ; the 

 margin in front and sides limited by an elevated and thickened 

 border, which is slightly extended at the posterior angles. Eyes 

 large, broad-oval, very prominent, situated near together, and 



* See Canadian Naturalist and Geologist, Vol. vii,. p. 443, December 1862. 



