BRACHIOPODA. 113 



valve, about the opening of the sipho. This feature is seen in all of Kutorga's 

 illustrations of the interior and internal casts of S. unguiculata, and would find 

 an equivalent in the umljonal swelling in Acrotreta, Acrothele and Linnars- 



SONIA. 



Of the muscular scars in this valve, the anterior probably represents the 

 anterior adductors, and the long impressions on either side of the sipho, termi- 

 nating in these anterior scars may be the progressive track left by them in the 

 growth of the shell. In the opposite valve, Davidson represents a transverse 

 posterior ridge, suggestive of the crescent in Trimerella, enveloping or ending 

 in distinct terminal scars, in front of which follow composite laterals divided 

 by a median ridge. Kutorga's figures show a sliglit median septum separated 

 by a furrow on either side from strong diverging ridges ; features which are 

 not widely different from the impressions in the corresponding valve of Lin- 



^fARSS0NIA. 



The Russian species of Siphonotreta (S. unguiculata, Eichwald, S. fornicata, 

 Kutorga, S. verrucosa, Verneuil, S. acukata, Kutorga, and (?) S. conoides, Kutorga), 

 are from the Lower Silurian faunas of the Baltic provinces ; S. micula, McCoy, 

 S. Scotica, Davidson, are from the Llandeilo flags, while the latest known repre- 

 sentative of the genus, S. anglica, Morris, is from the Wenlock. 



Genus SCHIZAMBON, Walcott. 1884. 



PLATE IV, FIGS. 27-30, COMPAKE FIGS. 31-36. 



1S84. Schizambon, Walcott. Monographs U. S. Geological Survey, vol. viii ; Palseontology of the 



Eureka District of Nevada, p. 69, pi. i, fig'. 3. 

 Compare : 

 1848. Siphonotreta, Kctokga. Verhandl. russ.-kais. mineral. Gesellsch. zu St. Petersburg. Jahrg. 



1847, p. 271, pi. vii, fig. 5. 

 1853. Siphonotreta, Davidson. Introd. British Fossil Brachiopoda, pi. ix, fig. 268. 

 1883. Siplionotreta, Whiteaves. Amer. Assoc. Advanc. Science, Montreal Meeting. 

 1SS3. Siphonotreta, Davidson. British Siluiian Brachiopoda, Supplement, p. 218. 

 1887. Siiihonntreta, Ami. Ottawa (Canada) Naturalist, December. 



Diagnosis. " Shell ovate or oblong-oval, inequivalve ; valves inarticulate ; 

 larger or ventral valve most convex, with a short obtuse beak at the cardinal 

 margin. Foramen oblong, and opening on the summit of the valve ; no area or 

 deltidium ; cardinal edge thin ; smaller or dorsal valve nearly as convex as the 



