380 THE PALEONTOLOGY OF MINNESOTA. 



(.Clltambonites diversa. 



of adductor scars. The antero-lateral edges of these are drawn out into short ridges, 

 probably the bases of the vascular trunks. Outside the muscular scars are a number 

 of small tubercles, indicating the genital spaces. 



This widely-distributed species was first described by Shaler as Orthisina diversa. 

 A year later Billings identified it as 0. verneuili Eichwald, at the same time regard- 

 Shaler's species as synonymous with it. On the other hand, Shaler has since referred 

 Orthisina verneuili Billings to his species, in which he is correct. On comparison 

 with the European species, as illustrated by de Verneuil,* it is seen that the 

 American species is wider along the hinge-line, the ventral area much less incurved 

 and elevated, with finer striae and a narrow sinus in the dorsal valve. These dif- 

 ferences are sufficient to distinguish the two species. Specimens of Hemipronites 

 americanus Whitfield have been collected at Oshkosh, Wisconsin, and are found to 

 agree with 0. diversa Shaler of the Hudson River group of Anticosti. Castelnau,** 

 as early as 1843, however, described as Terebratala borealis a shell derived from the 

 " magriesian limestone of Green bay, Wisconsin," which may prove to be this species. 

 The only illustration given is of a ventral valve, and this is not satisfactory for 

 positive determination. These type specimens are probably in the collections of 

 the Academy of Sciences at Paris, France. 



C. diversa must have been quite often the prey of other animals, probably gastro- 

 pods, as valves of this species are found with a single, large circular hole in them, 

 such as are often seen in recent shells. Others have been partially crushed, gener- 

 ally near the anterior margin. That such injury was received during life, but was 

 occasionally not sufficient to kill the animal, is shown by the fact that in some shells 

 the damage was repaired. Such specimens are irregular in growth, the place of 

 injury being indicated by more or less of a depression and great irregularity of the 

 striae. 



Formation and locality. Very common in the yellow shales here designated as Clitambonites beds 

 of the Galena shales. With this species many forms are introduced which extend upward, while a 

 number of species of the Trenton shales below do not pass into the Clitambonites horizon. A single 

 specimen has been found in the uppermost layer of the shales on St. Anthony hill, St. Paul. Common 

 at many localities south of Cannon Falls, Kenyon and Warsaw, Goodhue county; Eyota, and near 

 Fountain, Minnesota. In the Galena at Oshkosh, Wisconsin. In the Trenton group, Ottawa, Canada. 

 Also in division I of the Anticosti group, Anticosti. Some fragments of what appear to_be a new 

 species have been found by Mr. Ulrich one mile south of Burgin, Kentucky, in the middle Trenton 

 beds. 



Collectors. Miss C. E. Seymour, W. H. Scofleld, A. D. Meeds and the writers. 



Mus. Reg. Nos. 5308, 5586, 5847, 5853, 6765, 7951-7957. 



* Russia and the Ural Mts.. vol. ii. pis. xi and xn. 



"Essal sur Ic Systiime Silurien de I'ArnSrique Septentnonale, p. 40, pi. xiv, fig. 14. 



