12 LINKARSSON, BRACHIOPODA OF THE PARADOXIDES BEDS. 



Orthis Lindströmi is contined to the strata witli Paradoxides 

 Forchhammeri In these it is not rare at Kinnekulle and Lo- 

 vened in W^estrogothia, and at Södra ^löckleby in the island of 

 Oland. In Jemtland I have found it in loose stones at Lill- 

 viken. 



Orthis exporrecta n. sp. 



Pl. II, figs. 13—1», pl. III, figs. 20. 21. 



Circumference of the shell transversely oval or nearly semi- 

 circular; hinge-line shorter than the width of the shell; cardinal 

 angles rounded; front gently curvcd or nearly straight. Surface 

 covered with numerous radiating ribs, crossed by a large number 

 of extrem ely miniite concentric striiv, visible only under the 

 lens, and by a few more marked. The ribs increase in number 

 through interpolation, but rnost of them, though of very unequal 

 coarseness, begin at the umbone, where thcy are so subtle as to 

 be hardly discernible. The ribs are usually rounded and broader 

 than the interstices; sometinies though seldom they are somewhat 

 angular and narrower than the interstices. Ven trål valve Avithout 

 fold or sinus, very convex, most so near the beak and at the sides, 

 somewhat depressed in the anterior portion of the mesial part. 

 Beak pointed and directcd backwards. .Vrea high, but not Avell 

 visible in any specimeu. In the interiör the muscular impression 

 is small but deep, subrhomboidal, or curved anteriorly, surroun- 

 ded by a raised edge, and divided longitudinally by two linear 

 ribs. From the anterior margin of the muscidar depression two 

 slightly diverging shallow furrows extend a longer or shorter 

 space, while near the murgin there are several radiating furrows. 

 Dorsal valve very gently convex or almost flat, with a slight 

 mesial depression, shallowing and widening forwards. In the 

 interiör the cardinal process is triangulär, undivided, situated 

 between two widely diverging brachial plates. From under the 

 cardinal process a widish, flattened, mesial ridge extends a longer 

 or shorter space, separating the muscular scars, which are small 

 and indistinct. Those of the anterior pair are oblong and lon- 

 gitudinal, the posterior shorter and transverse. 



Some specimens measured: 



Length. Breadth. 



Ventral valve 8 mm. 10 mm. 



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