BRACHIOPODA. 
Ill 
Shell ornamented with concentric lines and ridges, the epidermal layer 
bearing hollow spines, which are distended at the base. Shell-substance cal- 
careo-corneous, the layers beneath the epidermis being punctured by radiating 
and branching tubules. These layers are concentric and not parallel to the 
internal surface. 
Type, Siphonotreta unguiculata, Eichwald. 
Observations. The foregoing description, with some essential modifications, 
is derived from the diagnosis of Siphonotreta, as given by de Verneuil, 
Kutorga and Davidson. The term as used by these writers, especially by 
Kutorga, has been allowed to include species which differ considerably in the 
position and structure of that feature of first importance, the pedicle-aperture, 
and these forms, under a proper conception of congeneric characters, it seems 
advisable to withdraw from the genus. 
In Kutorga’s elaborate study of Siphonotreta and its allied genera,* the 
position of the siphonal opening was considered as varying between the cardi¬ 
nal margin and the center of the valve. Strictly, however, the opening takes 
neither of these extreme positions in Siphonotreta, for in no species known is 
the umbo of the pedicle-valve marginal, and therefore the aperture, which may 
be regarded as always truncating the beak, can not be marginal. For the spec¬ 
ies Siphonotreta tentorium, Kutorga, in which both apex and aperture are at the 
center of the valve, the author himself suggested the name Mesotreta, and the 
term may be useful as designating a form intermediate between Acrotreta and 
Siphonotreta. Under the discussion of the genus Schizambon, reasons are given 
for provisionally adopting Mr. Walcott’s suggestion, that such species as Siphono¬ 
treta jissa, Kutorga, in which the external opening of the siphonal tube is situated 
in front of the apex and connected therewith by a conspicuous groove, should 
not be regarded as congeneric with S. unguiculata and other forms in which 
this aperture is circular and apical. Although there is considerable difference 
in the size and external expression of the type-species of Schizambon ( S. ti/picalis, 
Walcott,) and the Russian and Canadian representatives of Siphonotreta jissa, yet 
* Ueber die Brachiopoden-Familie der Siphonotretsese, p. 261, pis. vi, vii. 
