438 MOLLUSCA phylüm vi 



Order 1. PRIONODBSMACEA DalL 



Section A. Palaeoconcha p.p. Neumayr.i 

 Family 1. Solemyacidae. 



Shell soleniform, equivalve, low-heaJced, edentulous, gaping, with the anterior end 

 longer and the epidermis conspicuous, exceeding the valves ; area obscure or none ; Ligament 

 amphidetic, parivincular, usually internal posteriorly ; mantle lohes united ventrally, 

 attached in front to the periostracum and valves hy a hroad surface, leaving no distinct 

 pallial line ; a single posterior siphonal and anterior pedal foramen in the mantle ; 

 adductors sub-equal, with a thickened ray in front of the posterior scar ; animal dioecious, 

 marine, hurrowing. Devonian to Recent. 



Solemya Lam. Carboniferoiis to Recent, rare in all horizoiis. Janeia King, 

 shorter and less inequivalve, may include most of the Paleozoic species hitherto 

 referred to Solemya. Glinopistha Meek and Worthen, from the Carboniferous, is also 

 allied, and Dystactella Hall, is nnited with it by Zittel. Phthonia Hall, from the 

 Devonian, is placed here by Ulrich. Ächarax Dali, Mesozoic to Recent, has a purely 

 external ligament and no clavicle. 



Family 2. Solenopsidae Neumayr. 



Shell thin, elongate, equivalve, with very anterior heaks ; the hinge edentulous, ligament 

 parivincular, external ; pallial line not sinuated ; a ridge or groove radiating from the 

 beak to the lower posterior angle of the valves. Marine. Devonian to Trias. 



Sanguinolites M'Coy. Elongate, obliquely truncate behind ; beaks low, sculp- 



ture of concentric or broken lines, an- 

 terior adductor scar buttressed by a 

 ridge. Carboniferous. 



Promacrus and Prothyris Meek. 

 Pj,. 649 Carboniferous, 



Solenopsis pelagica Goldf. Devonian ; Bifel District. Ärcomyopsis Sandb. Somewhat 



curved, with prominent beaks ; obliquely 

 truncate behind; posterior area radially, the rest of the surface concentrically 

 sculptured. Devonian. 



Solenopsis M'Coy (Fig. 649). Very long, scabbard-shaped, smooth ; anteriorly 

 Short and rounded, gaping behind. Devonian to Trias. 



Family 3. Vlastidae Neumayr. 



Shell thin, very inequivalve, beaks elevated, hinge line edentulous, arehed, meeting at an 

 obtuse angle beneath the beaks, leaving a dorsal opening ; surface smooth or concentrically 

 striate. 



The two genera Vlasta and Dux (Vevoda) Barrande, from the Silurian of Bohemia 

 (Etage E 2), constitute this family. 



Family 4. Grammysiidae Fischer. 



Shell thin, equivalve, oval or elongate, with the beaks sub-central to anterior ; hinge 

 edentulous, sometimes thickened. Ligament parivincular, external; imllial line not 

 sinuate ; surface smooth or concentrically sculptured. Silurian to Carboniferous. 



^ [The terms Palaeoconcha, Taxodonta, Schizodonta, etc., preceded by Roman numei-als, are 

 retained here merely as convenient descriptive ai)pellations, and are in nowise to be regarded as 

 possessing systematic values.j 



