Description of a New Species of Stylonueus. 77 



GENUS STYLONUKUS, Page 1856. 



Stylonurus excelsior, n. sp. 

 Plate V, fig. 1. 



Carapace sub-elliptical, truncate behind; width at the base about 

 two-thirds of the length ; lateral margins gently curved outward from 

 the base of the carapace to a point opposite the base of the palpebral 

 archps, thence gradually incurving to the front of the carapace. 



Eyes circular situated on a line just anterior to the center of the 

 length; separated by a strong median ridge which, commencing 

 nearly on a line with the posterior limits of the palpebral arches extends 

 forward nearly one-half the distance to the anterior margin where it be- 

 comes merged in the general convexity of the surface ; palpebral 

 arches strongly elevated semi-circular, more regularly curving behind, 

 where they are gradually depressed into the general contour ; the an- 

 terior portion of the arch is narrower and terminates abruptly in aline 

 almost through the center of the eyes ; posterior angles of the cara- 

 pace rounded; occipital ring moderately defined, anterior to which 

 and separated by a transverse depression, is a central lobe with an in- 

 termediate and lateral lobe on each side with corresponding depres- 

 sions. 



Surface on the anterior part marked by strong elongate and conflu- 

 ent pustules which are arranged in concentric lines, becoming more 

 individualized and directed backward and subimbricating on the pos- 

 terior half ; the markings on the occipital ring are more subdued than 

 upon the general surface, except on the posterior margin which is 

 ornamented by a row of strong spiniform nodes; the entire interme- 

 diate surface, as well as the surface of the nodes, is marked by fine 

 scales ; the surface included by the palpebral arches is marked by 

 stronger scales which are not elevated into nodes ; the concave spaces 

 between the posterior lobes are marked only by the fine, scale-like or- 

 namentation. 



Abdomen and appendages unknown. 



The greatest length of the carapace is two hundred and fifty-five 

 millimetres ; width at base one hundred and ninety-five millimetres ; 

 width in a line through the bases of the palpebral arches two hundred 

 and twenty-five millimetres, and across the anterior extremities of the 

 arches one hundred and ninety-three millimetres ; the diameter of the 

 eyes is twenty-three millimetres ; distance between the extremities of 

 the palpebral arches, sixty-five millimetres. 



This species is very different from the ordinary forms of the genus 

 in the great anterior extension of the carapace and the prominence of 

 the palpebral arches. 



A restoration on the scale of Stylonurus Logani, Woodward, would 

 make the entire animal over four feet in length. 



Formation and locality. In the Oatskill group; Andes, Delaware 

 county, N. Y. 



