1846-] MORRIS ON TEREBRATULA. 389 



nate divisions of each of the sections above-proposed ; thus we find 

 among the Hypothyridae the T, affinis and T. aspera, which with 

 an embracing area have a spiral apophysary system vertically placed, 

 whereas in the Pugnacese and Concinnse this system becomes vari- 

 ously modified, and more or less strongly developed. In the Epi- 

 thyridae the T,ferita has also a spiral apophysary system, but late- 

 rally placed as in the Spiriferse ; in the T. digona (Cinctee) the two 

 internal pieces simply diverge towards the margin, and are again 

 reflected and joined posteriorly ; in the Jugatae ( T. carnea) this sy- 

 stem is more modified, and resembles somewhat that of T. vitrea of 

 the existing period ; and many other diversities of form of this part 

 may be well studied in the different recent species belonging to this 

 section. 



It will be observed in the above notice, that a small group of 

 shells generally arranged among the Terebratulae, the T. concentricce^ 

 have been omitted ; these species possess only a small deltidial area 

 without any foramen*, are wider than long, with no cardinal area, 

 are concentrically striated or laminated, non-punctated, and fur- 

 nished with a spiral apophysary system laterally developed, as in 

 Spirifer. Mr. J. Sowerby, in adopting the genus Atrypa, has di- 

 vided it into three sections, under one of which he has included the 

 small group of shells above-mentioned; and however different in 

 character from the species previously classed by Dalman under the 

 same name, there can scarcely be any doubt that they differ con- 

 siderably from the true Terebratulse, and form a passage into the 

 group of the smooth Spirifers, the " SpirifercB glahratce" of Professor 

 Phillips. Mr. M'Coy has constituted the generic term Athyris for 

 their reception, and placed them with the Spirifers under the Del- 

 thyridae. 



In the other Terebratuliform genera, Pentamerus, Strigocephalus 

 and Magas, the opening for the passage of the muscle of attach- 

 ment is always within the deltidial area ; in Pentamerus it is how- 

 ever partly concealed by the curvature of the dorsal valve ; in Stri- 

 gocephalus the deltidium is more fully developed, and in one species, 

 S.dorsatus, entirely surrounds the circular or oval foramen; the struc- 

 ture of the shell is fibrous, and the inner layer is somewhat punctated, 

 whereas in Pentamerus it is more laminated : in both these genera 

 the apophysary system is singular and distinct. Magas apparently 

 presents an anomaly in its general characters ; for with a deltidial 

 opening beneath an acute beak, it possesses a punctato-tuberculated 

 structure (the opposite characters in the two groups of Terebratulae 

 being here combined), and a rather complex apophysary system. 

 This genus is probably more nearly allied to some species of Orthidoe, 

 as O. elegantida^ which has also a similar punctated structure, with 

 a deltidial opening, but a simpler apophysary arrangement. 



* Many of the published figures of these species represent thcni as having a 

 circular foramen, but I feel convinced that this appearance is dccei)tive, and that 

 tlie beak is entire and not perforated. 



