166 PROCEEDINGS OF THE ACADEMY OF [1889. 



DESCRIPTION OF NEW SPECIES OF FOSSIL CRUSTACEA FROM 



THE LOWER SILURIAN OF TENNESSEE, WITH REMARKS 



ON OTHERS NOT WELL KNOWN. 



BY J. M. SAFFORD AND A. W. VOGDEiS. 



Ampyx Americanus, n. s. 



General outline broadly oval, glabella some- 

 what claviforin, slightly convex, narrowing 

 ....■' ..... behind the middle and widening out slightly 



at its junction with the occipital ring ; it is 

 marked at each side by one or more oblique 

 furrows, the condition of the three specimens 

 before us do not clearly indicate more than 

 one pair. Projecting spine broken off. The 

 cheeks are broad and rounded towards the 

 margins. Genal spines broken off. Facial 

 sutures not observed. 



The axis is broad anteriorly and gradually 

 diminishes, being well denned by its broadly convex form ; the rings 

 are deeply furrowed centrally. The pleura? are six in number, 

 straight and deeply grooved, terminating in obtusely pointed points, 

 similar to those of Ampyx nudus. [Barrande Syst. Sil. Boheme, 

 Vol. 1, PL 5, fig. 14.] 



The pygidium is triangular in form, the axis being prominent, 

 gently tapering to an obtuse point on the posterior border. It is 

 marked with 13 or more rings, with a central row of nodes. The 

 sides have only one pair of side ribs, which are deeply furrowed out- 

 wards cutting off the posterior portion of the tail. 



Geological position and locality, Trenton group, near Bulls Gap 

 on the road to Russelville, Tenn. Cabinet of J. M. Safford. 



Affinities : We have compared the Tennessee species with the 17 

 described species of the genus Ampyx and find that it differs in 

 detail from all of them. It has affinities with Ampyx nasutus, Dalrn. 

 which has the same number of thoracic segments, its pygidium being 

 marked with only one lateral side furrow on each side. From this 

 A. Americanus can be readily distinguished by its glabella, broader 



