142 Thr Lifi'-Hhforii of Spirifer hpru. 



in general appearance it is readily distiuguished from any earlier 

 form. 



Comparing it with European forms of the Carboniferous, it 

 appears as one of them ; and in general Spirifer kevis, H. pre- 

 sents greater resemblance to the Carboniferous than to the De- 

 vonian representatives of the genus. 



As a well-marked form, with a limited geological horizon, 

 and appearing in a limited geographical area, Spirifer Icevis is 

 interesting in itself; and a study of its relations to the past, be- 

 comes especially interesting, on acdount of its appearance here 

 in the Portage, as a new and distinct "species," and in its dis- 

 tinctive characters, seeming to belong to a type or form entirely 

 new for the genus. It stands out prominently as a suddenly 

 appearing "species;" and between it and the forms preceding it 

 there appears, at first sight, to be a distinct gap. Without 

 attempting to redescribe the species, it may be worth while to 

 point out its distinguishing characters. 



Form and Fro])0)iions. — The outline of the ventral valve, the 

 one more commonly met with, is sub-circular or semi-elliptical, 

 with prominent beak and broadly rounded margins at the car- 

 dinal extremities, the margins of the shell almost always crushed 

 and generally distorted. Opposite the beak, the base of the 

 sinus is generally folded under, and thus this margin appears 

 truncated, es|)ecially in larger shells. The greatest Avidth of the 

 shell is in a line lying anterior to the cardinal line about as far 

 as the beak extends posterior to it. Over this same line is the 

 greatest elevation of the swollen valve. 



The proportions of length to breadth are, as Hall mentions, 

 "from two to three, or three to four."' In specimens of which the 

 sinus IS preserved to the end, I find the distance measured on 

 the outer surface of the shell, from the point of the beak along 

 the groove of the sinus to its anterior margin, is very nearly equal 

 to the greatest actual breadth of the shell. This line measures 

 the actual length of superficial groAvth in the medial line of the 

 ventral valve, and thus becomes a very fair unit of measurement 

 for comparison, and can be determined as w^ell in distorted as in 

 uncrushed specimens. 



