Report of the State Geologist. 



559 



cardinal area and separated by a more or Less developed median 



septum extending to about the renter of the v;tlve The 

 ••laterals"' are well developed and occupy a position not equiva- 

 lent to the impressions in Obolella which have been designated 

 by this term, but more nearly to that of the terminal soars of the 

 crescent in Dinobolus. The median area of the valve on each 

 side of the septum is much thickened, and at its anterior edge lie 

 the conspicuous central scars. In the brachial valve the cardinal 

 and " lateral " (external or terminal) impressions are developed 

 as in the opposite valve, and in the central region is a pair of 

 curved impressions. These inclose an indistinct central scar. 



Larger valve. Smaller valve. 



Figs 244,245 — Diagrammatic view of Obolus Quenstedti. After Mickwitz. 



a, Pedicle-groove; 6, impression left by the advance of the lateral sliding muscles; c, median 

 septum; d, cordate pit; e, sinus; /. median groove; g, median swelling; 7i, lateral grooves; 

 i, impressions of vascular trunks; A-, impressions of secondary sinuses; I, impressions of 

 posterior adductors; m, impression of anterior adductors; n, impressions of sliding muscles ; 

 o, outline of splancbnoccele; I, splanchoccele ; II, brachiocoele , in, pleurocoele 



Type, Obolus Ajpollinis, Eichwald. Cambrian (Unguliten- 

 schichten). 



Mickwitz has elaborated the internal impressions of his species 

 Obolus Quenstedti, showing that it possessed a very complicated 

 muscular system not unlike that of Lixgula. It is, however, not 

 satisfactorily demonstrated that this species is a true Obolus. 



Aulonotreta, Kutorga. 1848. 



Synonym ; Acritis, Volborth, 1869. 



(This name was proposed to take the place of Obolus, Eichwald, 



1829. The first type is A. polita, Kutorga = Obolus Apollinis, 



Eichwald; the second, A. sculpta, Kutorga^ 0. antiquissi?nus, 



111 



