568 



Fortt-fixTB Report on the State Museum. 



merited by concentric growth-lines bearing spines. Pedicle- valve 

 only known. 



Type, Mesotreta tentorium, Kutorga (Lower Silurian. Russia.). 



Trematobolus, Matthew. 1893. 

 Shell biconvex ; valves lenticular. Pedicle-valve with a low, 

 striated hinge-area, the anterior margin of which bears two small 

 articulating apophyses or teeth. Foramen in the center of the shell, 

 opening obliquely backward ; between it and the apex is a long 

 tapering groove, with a corresponding ridge on the interior. Muscu- 

 lar scars submarginal, divisible into a posterior and anterior pair. 



cp c % 



Fig. 263.- Trematobolus insignis. la, interior of pedicle-valve; 16, internal cast of brachial 

 valve; lc, cardinal view of brachial valve; Id, inside of beak of pedicle-valve; pa, posterior 

 adductors: ad, adjustors; Im, lateral muscles; t, teeth; /, foramen; s, sockets; c, cardinal pro- 

 cess; cp, cardinal pits. (Matthew.) 



Brachial valve, with long, narrow dental sockets and distinct 

 cardinal process. Anterior and posterior muscular scars submar- 

 ginal and less remote than in the opposite valve. 



Surface covered with fine concentric growth-lines and faint 

 traces of radial stria 1 . 



Shell substance calcareo-corneous (?) 



Type, Trematobolus Ins ign is, ft I a ttli e w . 



Distribution. St. John group : Hanford Brook, ISTew Brunswick. 



Siphonotreta* de Verneuil. L845. 



(Plate 4, Figs. 22-26.) 



Shell elongate-oval, Lnequivalve; valves unarticulated. Pedicle- 

 valve the more convex, with a straight, elevated, conical, and 

 perforated beak, the circular foramen opening at the apex and 



L20 



