ADDENDA. 48a 



From the external character of the species referred by me (o Atryjta aprinis, 

 Palseont. New-York, Vol. ii, pa. 280, pi. 57, f. 7 ( = Terebratula a-prinis, M. V. K. 

 Geol. Russia and the Ural Mountains, Vol. ii, pa. 90, pi. x, f- 10), I infer that it 

 belongs to this genus, and the name Rhynchospira apriniformis may be adopted for 

 it, since the American and European forms are probably distinct. 



Rlijncliospira formosa. 



Plate XGV A. Fig. 7 - 11. 



Fig. 7. Interior of the ventral valve of Rhynchospira formosa. 



Fig. 8. Interior of tlie dorsal valve, enlarged two diameters, to show the broad cardinal 

 process (j), which covers the extremity of the beak, and, when the valves are 

 closed, passes beneath the deltidial area of the opposite valve. The bases of the 

 crura (f) are shown on each side at the base of the cardinal process, and the 

 short median septum is shown at s. 



Fig. 9. Profile view of the same, showing the cardinal and crural processes. 



Fig. 10. The upper part of the two valves connected in their natural relations to each other, 

 and showing the manner of articulation. 



Fig. 11. A longitudinal section, showing the foramen, the deltidium, and the cardinal process 

 of the opposite valve lying beneath it ; the crura first bending downwards, and 

 then recurved into the dorsal valve and its continuation in the spire, witli the 

 descending process e, which forms, with the opposite one, a connecting filament 

 between the two spires. 



Rliyncliospira rectirostra ( page 217). 



Plate XCV A. Fia. 1 a, 6, c ( These figures are referred, at page 217, to 

 Plate XXXVI a, fig. 1 a, b, c.) 



CAMARIUM. 



Among the fossils referred by me to the Genus Merista, and published 

 in the Report of the Regents of the University in 1856 and 1857, and 

 printed in this volume in the year last mentioned, are several, which, 

 although possessing the general form of Merista, present nevertheless 

 some noticeable peculiarities. One of these is the strongly incurved beak 

 of the ventral valve, while the cardinal margin is abruptly bent inwards, 

 leaving an angular or subangular ridge extending from the beak to the 

 margin of the shell, the space between this and the cardinal margin being 

 sometimes flattened about halfway to the base. The front of the shell is 

 often produced in a broad linguiform extension of the ventral valve : 



