438 



MOLLUSCA 



PHYLUM VI 



Order 1. PRIONODESMACEA Ball. 



Section A. Palaeoconcha p.p. Neumayr.^ 

 Family 1. Solemyacidae. 



Shell soleniform, equivalve, low-beaked, 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 lobes united ventrally, 

 attached in front to the periostracum and valves by a broad surface, leaving no distinct 

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

 adductors s^ib-equal, with a thickened ray in front of the posterior sear ; animojl dioecious, 

 marine, burrowing. Devonian to Kecent. 



Solemya Lam. Carboniferous to Eecent, rare in all horizons. Janeia King, 

 shorter and less inequi valve, 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 united with it by Zittel. Phthonia Hall, from the 

 Devonian, is placed here by Ulrich. Acharax Dall, Mesozoic to Recent, has a purely 

 external ligament and no clavicle. 



Family 2. Solenopsidae Neumayr, 



Shell thin, elongate, equivalve, with very anterior beaks ; the hinge edentulous, ligamient 

 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 

 Carboniferous. 

 Promacrus and Prothyris Meek. 

 Carboniferous. 



Arcomyopsis Sandb. Somewhat 

 curved, with prominent beaks; obliquely 

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

 sculjitured. Devonian. 



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

 short and rounded, gaping behind. Devonian to Trias. 



' ridge. 



Fig. 649. 

 Solenopsis pelagica Goldf. Devonian ; Eifel District. 



Family 3. Vlastidae Neumayr. 



Shell thin, very inequivalve, beaks elevated, hinge line edentulous, arched, 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 ; 'pallial line not 

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



' [The terms Palaeoconcha, Taxodonta, Schizodonta, etc., preceded liy Roiiiau numerals, are 

 retained here merely as convenient descriptive ajipellations, and are in nowise to be regarded as 

 possessing systematic values.] 



