BRACHIOPODA. 
46 
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 impunctate outer layer seems to become thinner in the 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 Dimidiates,,^ 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 uncinata, Schlotheim, S. austriaca, Suess, N. 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 palaeozoic 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 Bittner f 
from the St. Cassian beds under a new generic designation, Cyrtotheca ((7. Ampez- 
zana), a minute shell whose size alone is indicative of an immature condition. 
^Beitrage zur Palaontologie Oesterreich-Ungarns, End. 1, 1882: Untersuchungen ueber rhatische 
Brachiopoden, p. 25. 
t Brachiopoden der Alpinen Trias, p. 116, pi. xxxviii, fig. 19, 1890. 
