324 bulletin: museum of comparative zoology. 



17. Leperditia abbreviata Schmidt. 



18. Calymene frontosa Lindstrom. 



19. Encrinurus punctatus. 



20. Goldius estonicus Schmidt. 



21. cf. marklini AngeUn. 



22. Illaenus livonicus Holm. 



23. proles. 



24. Phacops elegans. 



25. Proetus concinnus Dalman. 



St. Johannis formation. By Schmidt this formation was desig- 

 nated the Lower Oesel zone, or stage I. It makes its first appearance 

 on the mainland just west of the village of Fennern, where it overlies 

 the Addifer formation and appears from beneath the Devonian. It 

 forms the surface rock of the north end, and probably most of the 

 central and southern parts of Moon, and all of the northeastern half of 

 Oesel. The exposures of the mainland are negligible; but on the 

 islands there are many and no difficulty need be experienced in ob- 

 taining a representative collection. Several of the best localities are 

 the island of Schildau between Moon and the mainland, St. Johannis 

 on the northeast corner of Oesel and Mustel or Panga Pank (cliff) on 

 the northwest corner. It is the only Silurian formation of this region 

 of which a nearly completely continuous section is shown. 



The formation has a thickness of about 100 feet, consisting of a 

 variation of dolomites and limestones interbedded with highly cal- 

 careous shales. As has been pre\'iously noted, perhaps there are beds 

 of sandstone in the lower part of the formation in its eastern exposures. 

 In the western areas manv of the beds are markedlv dolomitic, and 

 some of the dolomitic beds carry hardly any fossils. 



Nearly the entire formation is shown at Mustel Pank on the north- 

 west coast of Oesel. At sea-level (Schmidt, 1858, p. 60) are beds of 

 limestones which are chiefly composed of corals. These are succeeded 

 by gray or blue calcareous shales rich in fossils. There are probably 

 not more than ten feet of these. Above follow compact gray lime- 

 stones with shale partings, and this zone traced horizontally appears 

 to pass over into gray or yellow, often porous, crystalline dolomites. 

 Somewhere in this Mustel Pank section is said to be the horizon of 

 the occurrence of Schidosteus mustelensis Pander. 



One of the most westerly of the good fossil localities, and one of the 

 few of the mainland was Kerkau which Schmidt ^ considered to lie at 



1 Schmidt. Loc. cit., 1858, p. 61. 



