64 OLAF HOLTEDAHL. M.-N. Kl. 



Stated, the presence of a »short row of cardinal denticulations«, the latter 

 existing only near the delth3^rium. 



In his paper on »The Anticosti Island Faunas« ^ p. 25 W. H. Twen- 

 HOFEL has proposed the subgeneric term Strophoprion for »those resupi- 

 nate forms of the Strophomenidae which are like Strophonella except that 

 they have some ten or a dozen denticulations along the hinge line instead 

 of a completely denticulated hinge margin. That is, these forms mark the 

 inception of the Strophonella stock, Strophoprion holding the same relation 

 to Strophonella that Brachyprion does to Stropheodonta«. It seems to me 

 that TwENHOFELS term Strophoprion must include much the same type of 

 forms for which Hall and Clarke has proposed the name Amphistrophia. 

 The fact that the Strophonella striata, the type species of Amphistrophia, 

 differs in some features, besides the character of the hinge margin, from the 

 typical Strophonella and thus also from Strophoprion, seems scarcely sufficient 

 to justify the establishment of Strophoprion as an indépendant subgenus, 

 different from Amphistrophia. As to the ventral muscular field of Amphi- 

 strophia striata, which is not bordered by any elevated ridge in front, 

 this feature is not as far as I can see sufficient for separating the form 

 from Strophonella or Strophoprion. In several Ordovicic resupinate Stro- 

 phomenids the muscular field has no bordering ridge in front, but they 

 cannot for that reason be separated from Strophomena. 



Amphistrophia Davidsoni, new name. 

 (PI. VII, fig. 6-7.) 



1 87 1. Strophomena eiiglypha His., Davidson, Brit. SH. Brach., p. 288 (in part.) pi. XL, 

 fig- 4-5- 



Mat. pres. A few dorsal and outer moulds of ventral valves in 

 rock, besides a fragmentary free specimen. 



Description. Shell of medium or rather large size, outline rather 

 elongate, more or less roundedly triangular. The dimensions of two speci- 

 mens are: 



Width 34 mm. 46 mm. 



Length 30 » 39 » 

 The deformed specimen figured pi. VII, fig. 6 belongs to a relatively 

 very broad type. Cardinal angles not completely preserved in any speci- 

 men, but as can be judged from what is seen they are rather acute. Ventral 

 valve slightly convex in the umbonal region, then slightly concave anteriorly, 

 and at a distance from the hinge of about V5 the total length of the valve, 



' Geol. Surv. of Canada, Mus. Bull. 3 1914. 



