594 A. W. GRABAU LOWER ORDOVICIC FORMATIONS 



tetragona Pand. 



var. lata Pand. 

 abscissa Pand. 

 bocki Lamanski. 

 parvula Lamanski. 



Other brachiopods are : 



Porambonitcs broggcri Laraansky. 

 Plectella gracilis Lamanski. 



unicata (Pander). 



semiovata Lamanski. 



media Lamanski. 



eminens Lamanski. 



externa Lamanski. 



obtusa Lamanski. 



Besides these brachiopods there occur 



Orthoceras atavus Brogg. 

 Siphonia (?) cylindrica Eicbw. 



Lamansky finds that the brachiopods of this horizon are divisible into 

 two groups. The species of the first group are restricted to this horizon 

 and do not pass upward into the overlying limestone. Here belong 0. 

 recta, 0. striata, 0. christianice, and 0. boclci. Only two of these are 

 found in Scandinavia, where 0. christianice occurs in the Ceratopyge 

 limestone, while 0. recta has been found in the Obolus sandstone near 

 Gefle. The other species of Orthis, as well as those of Porambonites and 

 Plectella, extend upward into the overlying Planilimbata limestone, 

 where they are for the most part represented by closely related mutations. 

 Lamansky holds that the brachiopods referred to Orthis sp., Leptsena sp., 

 Strophomena sp., etcetera, from the Ceratopyge beds, and the intercalated 

 limestones of the Phyllograptus shales of Sweden may be of species above 

 listed. Those brachiopods are somewhat suggestive of species found in 

 the later Ordovicic (Trenton, etcetera) of North America and the equiva- 

 lent west European horizons, suggesting that this element of the fauna 

 had its center of distribution in the northeastern region, from which suc- 

 cessive migrant groups were sent westward throughout Ordovicic time. 

 We can, however, not follow Bassler in placing these lower deposits in 

 the Middle Ordovicic on the basis of these brachiopod types. 27 



Among the trilobites, Megalaspis leuchtenbergi shows the close relation 

 of this division to the succeeding beds with M . planilimbata; Triarthrus 

 angelini, on the other hand, is a characteristic species of the Ceratopyge 

 limestone of Sweden. The intimate relationship with the Phyllograptus 



27 Raymond also correlates these with the lowest Beekmantown. 



