MARYLAND GEOLOGICAL SURVEY 355 



and then again broadens out, becoming nearly as wide on the occipital 

 furrow as it was on the anterior margin; the two lateral lobes about as 

 prominent as the median lobe, subcrescentiform in outline. Dorsal fur- 

 rows concave inward, about as deeply impressed as the glabellar furrows. 

 Fixed cheeks rather broad along the posterior margin of the head, becom- 

 ing rapidly narrower to a point just behind the palpebral lobe; the palpe- 

 bral lobe rather prominent, the cheek becoming very narrow anteriorly. 

 Occipital furrow and occipital segment well denned, extending across the 

 fixed cheeks. The entire surface ornamented with small, low, rounded 

 tubercles, somewhat variable in size. Free cheeks, thorax and pygidium 

 unknown." Weller, 1903. 



The above description by Weller is the most detailed that has so far been 

 published, and as the specimens now under study show no additional 

 features both his description and figures are reproduced. 



Occurrence. MARTINSBURG SHALE (Sinuites bed). Carlisle and 

 Chambersburg, Pennsylvania, and Strasburg, Virginia. 



Collection. U. S. National Museum. 



Family ODONTOPLEURIDAE 

 Genus AGIDASPIS Murchison 

 ACIDASPIS TTLKICHI n. sp. 



Plate XXXVII, Figs. 6-8 



Description. The most interesting species in the fauna of the Fred- 

 erick limestone is a remarkably spinose trilobite represented by rather 

 numerous fragments of the free cheek with its extended genal spine. 

 Unlike most American species of Acidaspis and allied genera, the spines 

 on the free cheek of the present one continue to the end of the genal 

 spine. These spines are regularly and closely placed and are of consider- 

 able length along the free cheek. They decrease in length along the genal 

 spine, but they are still conspicuous at its end. Another unusual feature 

 is a great curvature of the free cheek with its genal spine, apparently 

 indicating that the latter were directed over the thorax of the trilobite. 



