18 LIXXAKSSO.V, BRACHIOPODA OF THE PARADOXIDES BEDS. 



from tlie Graptolite scliists which I can identify Avith the A. 

 socialis of the regio Conocorypharum. It seems probable tliat 

 from the tnie regio Conocorypharum also more than one species 

 has been referred by Professor T. Seebach to the A. socialis. 

 The exteriörs figured by him belong probably to the same spe- 

 cies for which I have retained the name, though I can see no 

 traces of the minute warts with which, according to him, the 

 surface is covered, and though the relative dimensions do not 

 quite agrec. On the other hand it does not seem improbable that 

 the description and figures of the interiör are made from specimens 

 of Oholella sagittalis. but they do not give an altogether clear 

 idea of the features which should be iUustrated. The two pro- 

 tuberances near the hinge margin of the smaller valve. which 

 are especially pointed out as something very characteristic, and 

 which are said to remind of the hinge teeth of the Terebratulida.% 

 might well be the projecting muscular scars of Obolella sagit- 

 talis. I must, liowever, repeat that I do not myself know the 

 interiör of Acrotreta socialis, and that, therefore, in this matter 

 I can set forth only a conjecture. 



As to the generic position, I can scarcely doubt that the 

 species is to be referred to the genus Acrotreta, though I have 

 not myself been able to discern the foramen at the apex. In 

 general shape it resembles very much the species formerly de- 

 scribed from Russia and Canada. but it is lower. From the 

 Russian type, A. siihconica Ivn.. it differs also by not having 

 any distinct groove in the false area of the ventral valve. 



Acrotreta socialis occurs chiefly in the strata with Parado- 

 xides Forchhammeri, in which it has been fbund at Kinnekulle 

 and Lovened in Westrogothia, and in tlie island of Bornholm. In 

 the strata with Paradoxides ölandicus, Dr. AVallin ha's found it 

 at Borgholm in the island of Oland. Pcrhaps it also occurs in a 

 limestone band between the strata with Paradoxides Kjerulfi and 

 those with P. Tessini at Andrarum in Scania. This limestone 

 band is crowded Avith fragments of Trilobites, especially a Para- 

 doxides, but they are so imperfect that it has not been possible 

 to dctermine any species. It cannot, therefore, at present be 

 settled to which division this limestone is to be referred. Be- 

 sides Trilobites it only contains an Acrotreta, which I cannot, 

 fi-om the imperfect materials, separate from A. socialis, and an 

 Acrothele, which will be referred to in the sequel. 



