42 G. F. MATTHEW ON THE 



part of the shell is said to have a flatly rounded ridge. In all these cases the flattened or 

 groove-bearing ridge projects forward into the central cavity of the shell. 



The dorsal valve in our shell departs more widely from the type of Obolella in its 

 comparative smoothness within, as well as in the absence of an area. Beside the linear 

 scars along the lateral edges the only marked, feature is the sharp little ridge within the 

 umbo. No such ridge is figured for any of the Obolella unless it is O. gemma} 



I (!o not know of any shell similar to ours haviugbeen described from the Dictyonema 

 beds of Sweden, Norway or Britain. 



LINNAESSONIA, Wakott (1885). 



In connection with the sketch of the history of Obolella, given on a x>revious page, 

 the writer has referred to the separation of the above genus from it. 



Mr. Walcott included in it O. sagiltalis and 0. transversa. And there should be adJed 

 a species occurring in the Protospongia beds of Metis, P.Q., as well as O pretiosn of the 

 Sillery sandstones, which Mr. Ami states is a Linnarssonia. O. mher of the Paradoxides 

 beds of Newfoundland seemingly belongs here, and here also it seems necessary to place a 

 small brachiopod found with the preceeding species. It is closely allied to one which 

 the author has referred to O. [L.) misera, found in the Paradoxides beds at St. Martins, N.B. 



Linnarssonia belti. Dav. ? (PI. XII, figs. 7 a-c.) 



Shell oblately orbicular. Test corneous. 



The dorsal valve (?) resembles that of the shell (O. misera ?) in the zone 1 d oi the St. 

 John group, being like that of an Acrotreta in its internal markings. 



In the ventral valve we do not see the strong scars and V-shaped ridge at the umbo 

 of the typical forms of Linnarssonia, but in their place small scars, and two faint Y-shaped 

 lines extending from the umbo. 



Sculpture. — Surface of the shell marked with fine concentric and less distinct radiat- 

 ing lines ; or is smooth. » 



Size. — Length, 3 mm. ; width, 3 J mm. 



Horizon and Locality. — From fine gray shales in the Dictyonema beds (Div. 3 r) at 

 Navy Island, St. John Harbour. 



This little shell is distinguished from those that occur with it (except Acrotreta), not 

 only by its form, but also by the extreme tenuity of its test, thickened only at the umbo. 

 In this also it resembles the shell from Div. 1 d referred to above, and those of the genus 

 Acrotreta. 



This shell is referred provisionally to Obolella Belli, Dav., of the Lower Tremadoc in 

 North Wales," which is about the horizon of our species. Davidson remarked that the 

 " internal characters agree pretty closely with those of O. sagiltalis." On comparing 

 Davidson's figures of the ventral A'alves of O. {L.) Belti and O. (L) sagiltalis one may 

 remark différences similar to those which distinguish O. (L.) misera, Bill., from O. (L.) 

 transversa, Hartt., of the St. John Group. In O. Belti and O. misera the muscular scars are 



" U. S. Geol. Surv. Bull. 30,' pi. x, fig. 2. 



'' ' Geol. Mag.,' vol. v, No. 7, p. 310, pi. xvi, figs. 25-27. 



