Maryland Geological Survey 489 



towards apex, average depth 3 mm. in specimen 25 mm. long. Septa con- 

 cave, thin edge slightly curved dorso-ventrally. Aperture, siplmncle and 

 exterior not observed. 



Length 25 mm. : diameter of chamber of habitation 15 mm. 



A single specimen has been observed whose generic relations are very 

 insecure. 



Occurrence. — Heldehberg Formation, Coeymans Member. Devil's 

 Backbone. 



Collection. — Maryland Geological Survey. 



[Swartz.] 



ARTHROPODA^ 



Subbranch BRANCHIATA 

 Class CRUSTACEA 



Subclass TRILOBITA 



Order OPISTHOPARIA 

 Family PROETIDAE 



Genus PROETUS Steininger 

 Proetus pachydeematus Barrett 

 Plate LXXXIX, Fig. 1 

 Proctus pachydermatus Weller, 1903, Pal. N. J., vol. iii, p. 248, pi. xxii, figs. 

 16-21. 



Description. — " Head semicircular in outline, with a broad, flattened, 

 marginal border, the genal angles produced into sharp spines. Glabella 

 subtriangular, with a pair of small, disconnected, ovoid basal lobes, ob- 

 tusely pointed in front, bordered by a sharply defined dorsal furrow ; the 

 first and second pairs of lateral furrows are rather faint, slightly curved 

 and directed obliquely backward from the margin of the glabella ; the 

 third pair more prominent, curved, directed backward and connecting with 

 the occipital furrow by a less sharply defined depression. Cheeks convex 

 to the marginal border, the eyes opposite the third pair of lateral glabellar 

 furrows. Facial sutures making a sigmoidal curve from the anterior 



^ The authors responsible for the text of the Arthropoda are Indicated for 

 each species. 



