Trigoxia. 



CONCIIIFERA. 



181 



and a littlo narrower; beaks obtuse, and nearly central ; basal 

 lino a little arcuated. 



The Coal ^Measures, Coalbrook Dale, Staffordshire. 



+7. U.vio I'liASEOLUs. — ThoPhaseolaUnio, pLLXXXA''!!!. 

 fi" 21 •■'■' 



U. phaseolus. Sowerby, Geo. Tr. 2d Ser. V. \A. 39, fig. 11. 



Consider.ably elongated transversely ; anterior side very 

 short, and pointed ; posterior side lengthonod, obtuse, and a 

 little tlattenoil ; beaks obtuse, and hardly developed ; back 

 nearly straight ; base a little concave in the middle. 



The Coal Measures, Coalbrook Dale. 



48. Unio robustus. — The Strong Unio, pi. LXXXVIII. 

 fig. 16. 



U. robustus. Sowerby, Geo. Tr. 2d Ser. V. pi. 39, fig. U. 



Sub-conic, convex ; beaks nearly central and obtuse ; both 

 sides sloping almost equally from the beaks ; the anterior one 

 large and rounded ; posterior side a little narrowed ; basal line 

 convex ; surface with strong lines of growth. 



The Coal Measures, Coalbrook Dale. 



49. U.VIO LiTTORALis. — The Shore Unio, pi. LXXXVIII. 

 fig. 7. 



U. littoralis. Drapernaud, pi. 10, fig. 20. 



Oblong-ovate ; much inflated ; anterior side very short, and 

 terminating rather abruptly ; beaks obtuse ; back considerably 

 arcuated ; a little narrowed at the lower posterior end ; basil 

 line a little concave; surface with nearly obsolete, shallow 

 lines of growth. 



The Coal Measures, Bradford. 



50. U.Nio DOLOBRATUs. — Squared Unio, pi. LXXXVIII. 



fig- 17. 



IT. dolohratus. Sowerby, Geo. Tr. 2d Ser. V. pi. 39, fig. 9. 



Sub-quadrate ; rather flat, with an oblique convexity along 



tlie middle ; anterior side exceedingly short ; posterior side 



lengthened ; hinge-line a little curved, base oblique, surface 



rather uneven. 



The Coal Measures, Coalbrook Dale. 



51. Unio aciuilinus. — The Eagle's-beak Unio, pi. 39, 

 I.XXXVIIL fig. 23. 



U. wiuV'inus. Sowerby, Geo. Trans. 2d Ser. V. pi. 39, 

 fig. 12. 



Transversely oblong-ovate ; beaks very small ; anterior 

 side very short with a small terminal projection ; posterior 

 side lengthene<l and pointed ; hinge-line a little curved ; back 

 and base slightly convex ; surface with transverse, rather rag- 

 ged ridges. 



The Coal Pleasures, Coalbrook Dale, StafTordshire. 



52. Usio PARALLELus. — The Parallel Uuio,pl. LXXXVIII. 



fig. 25. 



U. paralleluf. Sowerby, Geo. Trs. 2d Ser. V. pi. 39, f. 8. 



Transversely elongated, sub-quailrate, and somewhat flat- 

 tened ; beaks nearly terminal, from whence the side abruptly 

 descends in a slightly oblique line ; posterior side, back 

 and basal line straight, and parallel to each other ; surface 

 with well-marked concentric lines of growth. 



The Coal Measures, Coalbrook Dale. 

 53. Unio discrepans. — The Discrepant Unio, pi. 

 LXXXVIII. fig. 21. 



Transversely oblong-ovate, and much inflated ; beaks ob- 

 tuse; hinge-line a little curved and oblique; anterior side 



rounded and of medium length ; a slight hollow below the 

 beaks ; posterior side elongated ; sub-truncated and contract- 

 ed at the termination ; back somewhat arcuated ; basal line 

 arcuated ; a littlo concave near the posterior side. 



The Coal Jleasuros, Low Moore, near Bradford, Yorkshire. 



5-i. Unio sub-constrictus. — The Sub-constricted Unio, pi. 

 LXXIV. figs. 15, 17. 



U. suh-ciiiiatrictus. Sowerby, I. p. 83, pi. 33, figs. 2. 3. 



Oblong-ovate, beaks sub-central, incurved and approximate .' 

 posterior side lengthened ; contracted near the end ; anterior 

 side rounded ; hinge-line sub-triangular, a sub-constriction, or 

 oblique groove running from the beaks to the margin ; basal 

 line arcuated interiorly, and a little concave posteriorly ; sur- 

 face smooth, with some shallow concentric furrows. 



In the Argillaceous Ironstone, Derbyshire. 



55. Unio uniformis. — The Uniform Unio, pi. LXI. "'■*"" 

 fig. 23. 



U. uniformis. Sowerby, I. p. 83, pi. 23, fig 4. Mya omlis, 

 Martin, Pet. Derby, pi. 27, fig. 28. 



Transversely oblong ovate ; beaks sub-central ; anterior 

 side a little rounded, posterior side slightly acuminated ; hinge- 

 line triangular; surface smooth, with a few shallow transverse 

 lines of growth. 



In the Clay of the Middle Oolite, Felraersham, Bedford- 

 shire, and Derbyshire. 



Genus V.— ALASMODON. — Say. 



Shell thick, generally transversely elongate, but variable in 

 form, equivalve, inequilateral; a little gaping posteriori v ; 

 with or without auricles ; unibones for the most part rough 

 and decorticated, more so anteriorly ; hinge with a lamellar, 

 blunted, lateral tooth on the posterior side, situate under the 

 ligament, but destitute of one on the anterior side ; a short, 

 irregularly indented, cardinal tooth in the right valve, which 

 locks between the two irregularly crested teeth in the left 

 valve ; ligament exterior and much elongated ; muscular im- 

 pressions large, irregular, frequently double, and placed near 

 the extremities ; pallial impression deepiv defined. 



1. ALA.SM0DON VESTUSTAS. — The Ancient Alasmodon, il. 

 LXXIL* fig. 19. 



Pachyodon testustss. Brown, Ann. Xat. Hist. 184.3. pi. 

 16,* fig. 7. 



Transversely elongated, conipressed ; umbones very obtuse 

 and depressed ; anterior side short and sub-acute ; posterior 

 side long, broad, and rounded at the extremity ; hinge and 

 basal lines very slightly arcuated ; external surface with pretty 

 broad, shallow, coi;eentric wrinkles. 



In the Carbonaceous Shale, at (Jristhorpe. 



I consider this species as belonging to tlie genus Aiasmoilon, with 

 which it agrees in all its external characters. 



Tribe II.— TRIGONACEA. 

 Primary teeth lamelliform, and transversely striated. 



Gends VI.— TUKjIOX 1 a.— Z?r«^«it7«. 

 Shell equivalve, inequilateral, transverse, trigonal, some- 

 times sub-orbicular ; cardinal teeth oblong, laterally compress- 



