MANUAL OF THE MOLLUSCA. 
vonceutrically striated. Dorsal valye with a longitudinal 
septum; upper part of the ventral valve with a deep sub- 
triangular muscular impression which unites with the rostral 
cavity. 
The species of this genus are Meriste without the peculiar 
appendage of the ventral valve. 
Distribution, 17 species. Silurian—Devonian. Europe, North 
America. 
The forms marked by plications on the mesial fold and sinus, 
and sometimes with obscure or distinct plications on the lateral 
portions of the shell, constitute the genus LEIORHYNCHUS, Hall. 
+ species. Devonian. United States. 
CHARIONELLA, Billings, 1861. 
Synonym, Cryptonella, Hall, 1861. 
Type, Athyris scitula. 
Shell resembling Athyris, but more elongate-ovate or ap- 
proaching to Terebratula inform. Internal spires asin Athyris - 
and Merista, but the dorsal hinge-plate is either obsolete along 
the middle, or anchylosed to the bottom of the valve. Foramen 
terminal, bounded on the lower side by one or two deltidial 
pieces, or by a portion of the shell. The mesial septum in the 
dorsal valve is either absent or rudimentary. 
Distribution, 15 species. Devonian. America, Spain. 
NUCLEOSPIRA, Hall, 1859. 
Etymology, nucleus, and spira. . 
Types, Spirifer pisum, Sowerby; Nucleospira vyentricusa, 
Hall, Figs. 21, 22, 23. 
Fig. 22. Fig. 23, 
Nucleospira ventricosa. 
Fig. 21, interior of the dorsal valve. Fig. 22, interior of the ventral valve. Fig, 23, 
interior of the dorsal valve, with a portion of the ventral valve attached. 
; J, cardinal process ; ¢ ¢, crural processes; 6 6, dental pockets ; 7, muscular impres- 
sions; 8s, medio-longitudinal septum; tt, teeth; 2-a flattened space or false area 
beneath the bezk. ( Hull.) 
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