PTYCHOPTERIA. 125 



Avicula Bodana, F. A. Homer, 1 appears to be more transverse, with a longer 

 hinge-line, larger wings, and a straighter posterior margin. 



Avicula Gervillei, (Ehlert, 2 is a shorter, deeper, and less oblique shell, with a 

 broader and less defined posterior region. 



Avicula serviens, Barrande, seems very closely to resemble it ; but its hind wing 

 seems generally rather shorter, and its surface sometimes retains fine rays ; and 

 it is therefore probable that it is distinct. 



2. LEIOPTERIA ? MURATA, n. sp. Plate XIV, fig. 8. 



Description. Right valve moderately small, flattish, transverse, oblique. Umbo 

 apparently rather acute, elevated. Anterior side rather broad. Antero- 

 inferior corner rather produced, broadly convex. Inferior margin wide, 

 gently and evenly convex. Postero-inferior corner produced, convex. Front 

 wing small, flat. Hind wing apparently large, broad, flat. Contour slightly 

 convex vertically, almost flat on the back horizontally. Surface covered by 

 regular, parallel, very distant, elevated ridges, which seem to incline backwards 

 from the margins, to be truncated by a narrow groove on their summits, and 

 to be separated by very wide and shallow smooth interspaces. 



Size. About 25 mm. high, 33 mm. long. 



Locality. A specimen of the right valve from Barnstaple is in the Woodwardian 

 Museum ; and one, which seems to be the mould of a corresponding left valve, is 

 in my Collection from Upcott Arch Quarry. 



Remarks. These fossils evidently appear to belong to a distinct species, but 

 they are unfortunately too imperfect to give a satisfactory conception of it. It 

 bears a curiously strong superficial resemblance to Ctenodonta lirata, so strong 

 that both specimens were at first mistaken for that shell. The likeness is, of 

 course, entirely deceptive. It is evidently a Leiopteria, though both in shape and 

 in ornament it differs distinctly from kindred forms. 



4. Genus PTYCHOPTERIA, Hall, 1883. 



It " differs from Actinopteria in the nasute anterior extremity, and large, straight 

 wing, marked by a strong longitudinal fold. Hinge-line narrow, linear ; furnished 

 with one or two linear, oblique, cardinal and lateral teeth. Surface with fine rays." 



1 1860, F. A. Eomer, ' Beitr. Harzgeb.,' pt. 4, p. 162, pi. xxv, fig. 9. 



2 1881, (Ehlert, ' Mem. Soc. Geol. Fr.,' ser. 3, vol. ii, p. 22, pi. iii, figs. 5, 5 a. 



