252 Annals of the Carnegie Museum. 



Description. 



Entire test oblong, the width about six tenths the length. Dorsal 

 furrows almost obsolete on the thorax, entirely so on the pygidium, 

 but fairly strong on the cephalon. One entire specimen is 60 milli- 

 meters long and 38 millimeters wide at the genal angles ; another is 

 83 millimeters long and 49 millimeters wide. 



Cephalon regularly rounded in front, with very slight constrictions 

 in front of the eyes. Free cheeks small, the eyes situated very far 

 apart and about half their own width from the posterior margin of the 

 cephalon. Neck ring faintly defined on the cast ; not distinguishable 

 on testiferous specimens. The dorsal furrows on the cephalon are far 

 apart, and rather faint on the test, but strongly defined on the cast. 

 Their course from the posterior margin is first diagonally inward for a 

 short distance, and then straight forward, until they merge into large 

 lunate markings, which, in the cast, appear as depressions. Thorax 

 of ten segments, which are smooth, rather wide, and nearly flat. At 

 the dorsal furrows, which are very far apart and almost obsolete, the 

 segments are bent downward and a little backward, but the deflection 

 is not abrupt as in other Illceni. The pygidium is large, regularly 

 arched, a little wider than long. It shows no trace of the axial lobe. 

 On the cast there are four or five transverse lines, suggestive of annu- 

 lations, and two rather large oval prominences which may correspond 

 to scars of muscular attachments on the inside of the test. 



This species differs from Bumastus trentonensis and B. milleriva. the 

 following particulars : the size is much greater, the dorsal furrows on 

 the cephalon are stronger, and on the thorax are further apart and 

 fainter, the cephalon is more strongly arched and incurved in front, 

 the lunate scars of the cephalon are further forward and stronger, and 

 the thoracic segments are proportionally wider. The most striking 

 difference is, of course, the size. Under most circumstances we would 

 not attach much importance to this, but our smallest specimen is twice 

 the size of the largest specimen of B. trentonensis figured by Clarke, 

 and none of the specimens of B. milleri from Ottawa, with nine seg- 

 ments, seem to exceed 30 millimeters in length. 



Locality. — So far as is known, this species is confined to the 

 Trenton Limestone. The specimens figured are from Hull, Quebec, 

 Canada, and are in Mr. Narraway's private collection. 



