348 SYSTEMATIC PALEONTOLOGY 



Occurrence. BEEKMANTOWN LIMESTONE (Stonehenge member). 

 Hagerstown and Funkstown, Maryland. 

 Collection. 1J. S. National Museum. 



Genus ONCHOMETOPUS Schmidt 

 ONCHOMETOPUS SIMPLEX Eaymond and Narraway 



Plate XLVII, Fig. 18 



Onchometopus simplex Raymond and Narraway, 1910, Ann. Carnegie Mus., 

 vol. vii, p. 51, pi. xvi, figs. 6-8. 



Description. " Cranidium moderately convex, slightly incurved at the 

 front. Glabella flat, obscurely defined, expanding in front of the eyes 

 and extending to the anterior margin; glabellar furrows absent, dorsal 

 furrows present back of the eyes, very shallow. Neck-furrow absent. 

 Eyes of medium size, situated a trifle more than their own length in front 

 of the posterior margin. Behind the eyes there is a small median tubercle 

 on the glabella. Free cheeks rounded at the genal angles. 



" Thorax of eight flat segments. Axial lobe a little more than one-third 

 the total width. Pleura with shallow grooves. 



" Pygidium rounded in outline, three-fifths as long as wide. Axial 

 lobe obscurely defined, the posterior end usually a little more prominent 

 than the other portions. There are no annulations. The surface is uni- 

 formly convex, without concave border. 



" This species is similar to Onchometopus obtusus (Hall) of the Chazy, 

 but the shell lacks the very coarse punctae of that form, and there are 

 fewer traces of glabellar furrows. It differs from Onchometopus susae 

 (Whitfield) in having a longer pygidium with a narrower and more 

 distinct axial lobe/ 



" Onchometopus may be readily distinguished from Isotelus by the 

 presence of a median tubercle on the glabella, the absence of a concave 

 border on both cephalon and pygidium, and by the somewhat narrower 

 axial lobe in the thorax." Raymond and Narraway, 1910. 



The interesting Maryland trilobite referred to the above species differs 

 from all other Chambersburg forms in the absence of the concave border 



