ART. 21 OEDOVICIAN TEILOBITES — ULEICH 27 



than any of the other American species. The outstanding structural 

 characteristic lies in the form and size of the fixed cheeks. The out- 

 line of these is more regularly curved and their convex areas broader 

 and more flatly convex than in any other species of the genus. On 

 the other hand, the outer pair of the frontal spines is uncommonly 

 weak, being reduced, as in T. fractus^ to mere angulations of the 

 thickened rim. The occipital ring is only moderately wide and the 

 neck spine exceedingly short and directed backward. Just in front 

 of the latter is a distinct rounded node that may represent the 

 " median eye " of Isotelus and many other trilobites. A minute body 

 similar to that described by Ruedemann as the lens of this probable 

 eye was observed in preparing the specimens. 



The convexity of the glabella is less than in specimens of most 

 of the other species of the genus, but this inferiority is regarded as 

 due in small part to reduction in rock mass by pressure subsequent 

 to fossilization. As in T. fractus and other species the convexity of 

 the glabella is greatest in the middle, the convexity of the lateral slopes 

 being appreciably lessened so as to produce an obscurely defined 

 median ridge. The entire surface of the glabella is loosely covered 

 with low tubercles that seem to be more plainly indicated on the 

 cast of the interior than on the outer surface of the test. Similarly 

 arranged but even lower pustules occur on the anterior half of the 

 gently convex areas of the fixed cheeks. A low ridge crowned with a 

 row of tubercles defines the outer limits of the convex areas and 

 assists in deepening the palpebral furrow. 



In general aspect T. latus reminds considerably of Angelin's 

 T. granulatus but is clearly distinct, attaining nearly twice the size 

 of that species and having a more conical glabella and wider as well 

 as less convex fixed cheeks. It also lacks the two large nodes or 

 spines on the anterior slope of the glabella and has a shorter 

 occipital spine. 



Occurrence. — This species has been found only in the limy basal 

 part of the Athens shale at the north end of the old limestone quarry, 

 nearly 3 miles southeast of Saltville, Va. Here it is associated with 

 Telephus spiniferus, Eohergia tnajor Raymond, Ampyxina powelli 

 Raymond, and various species of graptolites, including Nemagraptus 

 gracilis Hall. Although seemingly occupying the position of the 

 Whitesburg limestone, the fauna consists practically entirely of 

 Athens shale species and not of Whitesburg limestone fossils. Evi- 

 dently the zone of Robergia major belongs to the Athens and not in 

 the older Whitesburg formation. 



Holotype.—C^i. No. 80539, U.S.N.M. 



