BRACHIOPODA. 45 



of the group, and is a feature whose manifestation is confined to the epidermal 

 layer of the shell. In Cyrtina, on the other hand, even in the earliest species, 

 punctation appears to have permeated all the shell layers except the outer. 

 The impiinctate outer layer seems to become thinner in tlie later species, and 

 there are indications that it is at times quite wanting. As far as investiga- 

 tions show, all the palaeozoic forms now placed with Cyrtina agree in full with 

 the type of structure described in the foregoing diagnosis. No important 

 variations have been found in the arrangement of the internal lamellae, the 

 structure of the cardinal process, or brachidium. 



After the close of the palaeozoic period the representatives of this line of de- 

 velopment appear to have undergone some modification. Zugmayer has shown 

 that certain so-called Spiriferinas of the Rhaetic beds, of which he has consti- 

 tuted his group Dimidiata* have the same septal structure as Cyrtina, the dental 

 lamellae uniting to form a spondylium which is supported by the median septum ; 

 e. g., Spiriferina undnata, Schlotheim, S. austriaca, Suess, .S. Suessi, Winkler. 

 Such forms, with all the outward expression of Cyrtina, and its principal 

 internal peculiarity, are assuredly not Spiriferinas. They naturally evince 

 some variations from the palceozoic type of Cyrtina, as seen in the figures of 

 S. Koessenensis (pi. iii, fig. 5) and S. Suessi (fig. 18) given by this author, where 

 the cardinal process is not bilobed but finely multilobed as in most of the later 

 Spirifers, the brachial valve with a row of crenulations just within the hinge- 

 line, and the spirals united by a transverse jugal band rather than by an erect 

 anteriorly directed loop. As yet we have no satisfactory evidence that the 

 palaeozoic Cyrtinas were attached in early stages of growth by the calcareous 

 cementation of the pedicle-valve. The frequent distortion of the umbo may 

 be regarded as presumptive evidence of this fact, as in the genus Derbya 

 where early fixation did occur, though evidently not a necessary condition in 

 all species or individuals. An attached Cyrtina has been described by Bittnerj 

 from the St. Cassian beds under a new generic designation, Cyrtotheca (C. Ampez- 

 zana), a minute shell whose size alone is indicative of an immature condition. 



*Beitrage zur Palaontologie OestHi-reich-Ung-arns, Bnd. 1, 1SS2 : Unlersiu-hungen uelier i-hatische 

 Brachiopoden, p. 25. 



t Brachiopoden der Alpinen Trias, p. 116, pi. xxxviii, fig-. 19, 1890. 



