AhiTEAvEs] FOSSILS OF HAMILTON FORMATION OF ONTARIO. 40S 



uiiconstricted, mucli shorter than the septate portion ; siphuncle almost 

 central, small, and not encircled bj' an "elevated areola" at the septa 

 (as in 0. Marcellense, Hall), its elements between the septa unknown : 

 surface markings unknown, though all the casts of the interior that the 

 writer has seen are smooth and entirely devoid of a mpdian central 

 carina. 



The most perfect specimen of this species that the writer has seen was 

 collected near Thedford, in 1894, by Mr. Kernahan, who has kindly 

 presented it to the Museum of the Surv'ey. It is slightly imperfect at 

 both ends, and its termination anteriorly is both irregular and indefinite, 

 but its dimensions are approximately as follows : Total length, about 

 seven inches ; length of chamber of habitation, from two inches to two 

 inches and a quarter ; thickness, at the smaller end twenty-seven milli- 

 metres, at the larger forty-eight ; number of septa preserved, seventeen ; 

 distance between two contiguous sutures, about six mm. and a half at the 

 smaller end and eight mm. at the larger. 



The only other specimens that the writer has seen which are clearly 

 referable to this species, are three fairly good ones (two of which have 

 part of the body chamber preserved), and three fi-agments, collected at 

 Bartlett's Mills by G. Kernahan and C. Schuchei-t in ISO"). All six are 

 now in the United States National Museum, and are No. 20,442 of its 

 Catalogue of Invertebrate Fossils. In one of these specimens the sutures 

 of the septa are as much as nine and ten mm. apart. 



The shortness of the chamber of habitation is practically the only 

 character that is relied upon to distinguish this species from 0. Ana.:-. 

 The former is very similar in shape to 0. Mrirrrl/rnse, Hall, but that 

 species is described as having an eccentric siphuncle encircled by an 

 "elevated areola," and a median ventral carina on casts of the interior. 

 The specific name for the fossil now under consideration is suggested by 

 the fact that Thedford is in the county of Lambton. 



B. Shell small. 



B. 1. Siphuncle central, or nearly so. 



Ortiioceijas subdlatum (?) Hall. 



Cfr. Orlhocrrax siihiifatUM, Hall. 1S4;\ Geol. Surv. X. York, Ke|i. Third Iii.^tr., ]>. Its. 



ISCl. |le,eii|.t. New Species.if Fo.ssils, I't.e., p. 4fl. 

 1S(;2. Fifteenth Rep. N. Y. St,, f'.'il.. Nat. Hist., p. 77. 

 u H rr 1S7G. lUiLstr. l)e\-onian Fossils : Ce])lial'jpoda, t'xjil. 



of pi. r.>. 

 187'.l. Pal. N. York, vol. v., jit. 2, p. L'S.i, pis. .'!,s, tlfr. 

 3; S4, tigs. 1, 2, 4, i;-l(l; anil ,S(i, tigs. 1 and 2. 



