178 



The test is narrowly semicircular, is moderatly arched in front and at 

 the sides, but had a steep slope behind where it was attached to the next 

 joint of the skeleton. 



Nearly half way from the back on the right side there is a prominent 

 circular tubercle, and in a corresponding position on the left side an 

 abraded space of similar form. Faint furrows go ou^from those tuber- 

 cles, in front and behind them, toward the lateral margins of the test. 



The apparent eyelobes in this test are in about the position of the eyes 

 of Limulus, but farther back than the normal position in Eurypterus. 

 Aglaspis of Hall, from the Upper Cambrian of Wisconsin, has circular 

 eyes like the tubercles in this test, but they are much closer together, 

 and nearer to the front of the shield. 



Sculpture. The surface is very finely granulate and punctate. 

 Size. Length, 7 mm. ; width, 10 mm. 



** Horizon and locality. Sandy shale of Assise E. 3 f at Gillis, Indian 

 brook, Escasonie, N.S. Rare. 



Dr. J. C. Moburg has described a fossil from Sweden found in a hori- 

 zon corresponding to the Etcheminian terrane, which is not unlike this.* 

 He refers it doubtfully to the genus Kutorgina. Only casts of the organ- 

 ism have been obtained, so that the texture of the test is unknown. It 

 has round tubercles corresponding to the supposed ocular tubercles of this 

 form, but they are more anterior and closer together and so are more 

 nearly in the position where the eyes of the Silurian Eurypteroids are 

 placed. This species is represented as having a raised rim and is more 

 elevated behind than the Cape Breton form, but the articulating slope is 

 not so strongly marked. 



The two Etcheminian faunas, shown together in the above descriptions, 

 may be divided as follows : 



Lower Fauna. 



Characteristic Acrothyra signata. 



species of the A ep rfl 



twoEtchemi- At 



nian faunas. A. tarda. 



A. orta. 



Acrotreta papillata. 



A. lata. 



Leptobolus cf. collicia. 



Upper Fauna. 



Acrothyra proavia. 



A. prima. 



j\., crassa. 



Acrothele avia. 



-\-, - - "- -"-' - - 1 - p\l 1*6 IS* 



,A aba via 



A. proles. 



*0ni en nyupptackt fauna i block of Kambrisk Sandsten . (Geol. foren i Stockholm, 

 Bd. 14 Haft 2, 1892. 



