92 CANADIAN FOSSILS. 



II. Lepeeditia Canadensis,* Jones, a. Var. nana. 

 Plate XI. Figs. 6, 7, 9, 10. 



(Annals of Natural History, 3d series, vol. i. p. 244, plate ix. figs. 11-15.) 



Length ^, breadth -^\ inch. 



Small; somewhat variable in shape, but always retaining the 

 characteristic Leperditia-outline, with straight back, more or less 

 obliquely-rounded belly, and sloping dorsal angles. Carapace usually 

 short (the height or breadth being about two-thirds of the length), 

 somewhat variable in the amount of convexity (thickness), which is 

 usually greatest at the antero-ventral third. Surface smooth. Eye- 

 tubercle generally well marked, and muscle-spot often distinct ; but 

 occasionally the latter becomes involved in the nuchal depression, 

 and the former is sometimes obsolete. 



This is the smallest form of Lcperditia which I have yet met with. 

 It occurs in great numbers, together with Be^jrichia Logani in equal 

 abundance, in a dark-grey friable limestone, mainly composed of these 

 Entomostraca, fragments of trilobites and shells, at Grrenville and 

 near Hamiltonville in Hawkesbury, on the Ottawa. This Leperditia 

 limestone forms part of a band of limestone, about two feet thick, 

 which extends over a wide district!, and is of importance as marking 

 the position of a continuous band of rock holding nodules of phosphate 

 of lime which is beneath it ; it belongs to the base of the Chazy 

 limestone. 



This variety of L. Canadensis occurs also in a dark-grey, crystalline, 

 shelly limestone (of the Calciferous Sandrock) on the north side of 

 Grande Isle,| in the St. Lawrence. In two hand specimens of this 

 limestone a few separate valves and one pair of valves are present. 



Beyrichia Logani and Leperditia Canadensis, var. 7iana, occur toge- 

 ther in immense numbers, forming indeed a considerable portion of 

 the limestone rock in which they are chiefly found. I believe 

 that the former is not the young of the latter (although perhaps 

 the differences of shape and structure are not greater than such 

 as we find to occur between the young and adult forms of recent 

 Entomosti'aca and other Crustacea), because, where the allied Bexjri- 



* Referred to in Quart. Journ. Geol. Soc. vol. viii. p. 202 and p. 207. 



f " This rock, having been quarried for lime-burning in several places, has been 

 followed from Carillon to Grenville (thirteen miles)." Quart. Journ. Geol. Society, 

 vol. viii. p. 207; and Logan's Report Geol. Surv. Canada, 1851-52, p. 18. 



X Quart. Journ. Geol. Soc. vol. viii. p; 202 ; and Logan's Report, 1851-52, p. 15. 



