iJ^Sq.] SoleniscHs : Its Generic Character. 421 
inally been placed under Macrocheilus. Upon the characters 
mentioned, principally, Macrocheilus and Soleniscus have been 
separated. The former was considered to embrace all the 
Devonian and a few of the Carboniferous forms described 
under the genus ; and the latter the majority of the American 
Carboniferous species, generally known under the other gen- 
eric title. 
Of Macrocheilus there have been described from Europe 
nearly fifty species ; two-fifths of which are from the Devonian. 
From America thirty-four species have been named ; of these 
five are from the Devonian, three from the Lower Carbonifer- 
ous and the rest from the Coal Measures. The American 
Devonian forms are exceedingly rare ; and nothing beyond the 
original descriptions is known in regard to them. With one 
exception, they have been, in all probability, erroneously re- 
ferred to the genus. The species described from the Carbon- 
iferous of North America will doubtless be reduced, after a 
careful comparison, to one-half the number now recognized. 
Macrocheilus was founded by Phillips' in 1841, and under it 
were enumerated ^7/^^2w?/w breve Sow., B. imbricatum VhWW^s, 
B. acHtum Sowerby and three other species. Phillips, how- 
ever, expressly remarked that the first two of these properly 
belong to other groups, and that he regarded the third form 
as more typical. B. aciitiim Sow. hence becomes the type of 
the genus ; and was thus considered by de Koninck and other 
European writers. An examination of numerous specimens 
of Macrocheilus {Biiccinum) acntnm shows that the shell pos- 
sesses a more or less thickened lip, and a prominent revolving 
fold on the columella. De Koninck'^ long ago recognized this 
fact, stating that " La columelle est garnie d'un pli oblique et 
quelquefois de deux ; le second pli n'est que faiblement ex- 
prime et ne s'observe bien que dans les echantillons d'une con- 
servation parfaite." It thus appears that the form described 
as Bnccinmn acntnm by Sowerby is in all respects a typical 
Soleniscus and that therefore that genus and Macrocheilus are 
identical. 
'Pak^. Foss. Cornwall, p. 103. 
2 Desc. des Anim. Foss. de Belgique, p. 474- •='44- 
