32 Mr. W. King on certain Genera 



In the synoptical table the genera Spirifer, Martinia, Atrypa 

 and Strigocephalus are grouped under the family Spiriferida. By 

 restricting the family to these genera, I am led to believe that no 

 point is involved that can in any respect embarrass a natural 

 classification of the great class to which it belongs ; at the same 

 time, there is little doubt that it forms a remarkably homogeneous 

 group, inasmuch as its species, there is every reason for supposing, 

 were tenanted by a mollusk furnished with labial processes that 

 were immovably fixed to a pair of spirally folded supports. This 

 character of the labial processes is fully warranted by the recent 

 Terebratulas, in which the same parts are immovably fixed to a 

 more or less complicated loop. The spiral form of the labial pro- 

 cesses, their immobility, and their spirally folded supports, are 

 characters which eminently distinguish Spiriferidce from every 

 other Palliobranchiate family. 



The spiral-bearing shells are found under so many different 

 forms as to have induced some to arrange them under a number 

 of genera, but I am led to believe that the principal part of 

 them are inadmissible, having been founded on characters highly 

 fugacious, or transitional, and proposed without a due consider- 

 ation of the claims of previous writers : thus Cyrtia was not only 

 based on a highly mutable character, but it was anticipated by 

 Spirifer, the typical species of which (S. cuspidatus) possesses the 

 same characters as Cyrtia trapezoidalis — the type of Dalman's 

 genus. Delthyris and Trigonotreta are equally inadmissible on 

 the same grounds. Br achy thy r is, M'Coy, has been anticipated 

 by Choristites, Fischer, which is founded on too transitional a 

 character. Actino conchas, M'Coy, if admitted, would render ne- 

 cessary the separation into so many genera, of such shells as Atrypa 

 planosulcata, A. pectinifera, A. fimbriata, A. Roissyi, A. reticu- 

 laris and A. aspera, because their marginal plates are severally 

 planosulcated, pectinated, fimbriate, setigerous, flounced, &c. 

 And as regards Athyris, M'Coy, and Cleiothyris, Phill., they have 

 been anticipated by Atrypa, whose name, notwithstanding its 

 being in several cases a misnomer, ought not on that account I 

 conceive to be now discarded. Certain objections might be urged 

 against the genus Martinia of M'Coy, but they do not appear to 

 be sufficiently strong to prevent its adoption ; by its possessing 

 an area and an exposed deltidium, Martinia may be readily di- 

 stinguished from Atrypa — the genus with which it stands the 

 most chance of being confounded. Reticularia, M f Coy, does not 

 appear to possess characters sufficient to warrant its separation 

 from Martinia. 



Terebratula and Hypothyris. 

 Mr. James Sowerby was the first to draw a distinction between 



