Ravmoni) : Brachiopoda and Ostracoda of the Chazv. 219 



luarkrd hy iuihumdus coiicenlrii' liiu's of ^rowtli. A i)arliall\' exfoli- 

 ated spociiiicn shows nuinerous radiating lines extending to both the 

 front and to the sides. A single cast of a dorsal valve shows two of the 

 central muscle scars. 



This species may be distinguished from Lingida huronensis by the 

 backward convergence of the sides and the longer and narrower 

 form. From IJngtila braincrdi it dilTers in the same particulars and 

 also in the length of the frontal slope. 



An average sj^ecimen is 17 mm. long and 14 mm. wide. A dorsal 

 \alve is 14.5 mm. long and 13.5 mm. wide. A young specimen with 

 l)arallel sides is 8.5 mm. long and 6 mm. wide. 



Locality. — This species was originally described from specimens 

 found on Allumette Island. It occurs also at Aylmer and at the Hog 

 Back, near Ottawa, Canada, in the shales of the Aylmer formation. 



5. Lingula huronensis Billings. 

 Lingula Huronensis Billings, 1859. Canadian Naturalist and Geologist, Vol. IV, 



p. 433, figs, ga-gd. 

 Lingula Huronesis Billings, 1863. Geology of Canada, p. 124, fig. 48. 



This species was described from specimens found in the Black River 

 limestone at Lake Huron, and, according to Billings, similar specimens 

 were found at L'Original in the Chazy. There are no specimens of 

 this type in our collections, but Dr. Ami has listed it from the Chazy 

 in the region about Ottawa. 



Order Telotremata Beecher. 

 Family RHYNXHOXFLLID.F: Gray. 



Genus Camarotcechia Hall and Clarke. 



The Palaeozoic Rhynchonellidae have been divided into a number 

 of genera, but the diagnoses of the genera are based on so limited an 

 amount of material that it is often difificult to understand what are 

 the real characteristics. RhynchoneJla plena was referred by Hall 

 and Clarke to the genus Camarotcechia, but recenth" there has been 

 a tendency to refer it to Rhynchotrema. An examination of the 

 original descriptions of the two genera does not make exactly clear 

 what the differences are which separate them. 



Rhynchotrema was proposed by Hall in the 13th Annual Report 

 of the New York State Cabinet of Natural History, pp. 66-68, i860. 



