143 



Fig. 33. Fig. 34. 



Fig. 33. Cast of ventral valve of M. Barrisi. 



Fig. 34. Cast of ventral valve of M. Haskinsi} 



In the dorsal valve of M. Barrisi we have a hinge plate, 

 with a median septum reaching more than one-third the 

 length of the shell, and the same characters exist in M. 

 Haskinsi. In M. Boris the rostral cavity and muscular im- 

 pression of the ventral valve are much elongated, and re- 

 semble what I have heretofore shown in Meristelia Icevis. 2 

 The dorsal valve has a strong extended median septum and 

 hinge structure as in the other species. 3 



The proportions of length of rostral cavity and muscu- 

 lar impression, vary in different species; and the muscular 

 impression becomes much stronger and deeper in the older 

 shells, when the valve as before remarked becomes thick- 

 ened at the sides and towards the beak. This character 

 pertains to the limestone specimens, while those in the 

 Hamilton shales, as figs. 7 and 8, have thinner shells, and 

 less deep and strong muscular impressions. 



1 have already {Thirteenth Report on the State Cabinet, pp. 



l The casts of M. Barrisi and M. Haskinsi are obtained from solid speci- 

 mens by removing the shells, and therefore have not that sharpness of the 

 muscular marking.-; which we find in weathered casts. 



2 Palaeontology of New York, vol. lit, plate 39. 



3 In reclaiming these species of Meristella, I am not impugning the va- 

 lidity of the genus Chaeionella of Mr. Billings, for none of these have the 

 characters of the dorsal valve of Charionella as represented on page 274, No. 

 xxxin of the Canadian Journal, which is not only clearly unlike Mekistella, 

 but very distinct from any genus of Spiriferid-s: before described. 



