43 



fourth thoracic segment each bearing on the median lino a single, large 

 and prominent, transversely elongated tubercle, which is arcuate or 

 reniform at its base and somewhat bilobate at its summit. The lateral 

 diameter of each of these tubercles greatly exceeds the longitudinal, 

 and measui-ing at their base, the proportions of each tubercle may be 

 thus appi-oximately estimated ; that on the first thoracic segment, lat. 

 diam. four mm., long. diam. not quite one mm.; that on the third, lat. 

 diam. nearly five mm., long. diam. rather more than one mm. ; that 

 on the third, lat. diam. five mm., long, diam., two mm. ; and that on the 

 fourth, lat. diam. five and a half mm., long, diam., three mm. 



Telson produced into a gradually narrowing, slightly cui'ved, and 

 rather obtusely pointed linear spine, which seems to be triangular in 

 transverse section. 



Antennffi, endognaths and ectogaaths unknown, as is also the natm-e 



of the surface markings of the test of the thoracic and caudal segments. 



Entire length, including the telson, about seventy-five mm. (or three 



inches) ; length of carapace, twenty mm., greatest breadth of the 



same, twenty-seven mm. ; length of telson, fifteen mm. 



Blora, collected in 1881, by Mr. David Boyle, an intelligent and suc- 

 cessful collector of the fossils of the G-uelph formation for many years, 

 to whom the writer begs to dedicate the species. The specimen figured, 

 which has been kindly presented to the Museum of the Survey by the 

 Trustees of the Elora School Museum, is an impression in a rather coarse- 

 grained dolomite of the exterior of the upper surface of the carapace, 

 with the whole of the thoracic and caudal segments in situ. Although 

 the type and only specimen known is too imperfectly jii'cserved to 

 admit of as accurate a description as could be wished, the species, 

 nevertheless seems to be suflSciently well characterized by the single 

 large and peculiarly shaped tubercle placed on the median line of the 

 upper surface of each of its foui- anterior thoracic segments. 



