BRACHIOPODA. Ill 



Shell ornamcntod with concentric lines and rid<;es, the epidernia! layer 

 bearing hollow spines, which are distended at the base. Shell-substance cal- 

 careo-corneons, the laj^ers beneath tlie 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 Sipuonotketa, as given by de Verneuil, 

 KuTORGA and Davidson. The term as used \iy 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 Siimionotiikta and its allied genera,* the 

 position of tiie siphonal opening was considered as var^'ing between the cardi- 

 nal margin and the center of tiio 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 wliich 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 SchizaiMison, reasons are given 

 for provisionally adopting Mr. Walcott's suggestion, that such species as Siphono- 

 treta fissa, Kutorga, in which the external opening of the siphonal tube is situated 

 in front of the apex and connected therewith l)y 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 Scihzambon {S. typicalis, 

 Walcott,) and the Russian and Canadian representatives of Siphonotreta Jissa, yet 



* Uebei- die Biachiopoden-Familic iler Siphonotretjese, p. 261, pis. vi, vii. 



