Unio. 



CONCHIFERA. 



177 



1. Unio Gerardi.— Gerard's Unio, pi. LXXIII. fig. 23. 

 Piicht/odon Gerardi, Brown, Ann. Nat. Hist. Dec. IS'IS, 



pi. l.i. figs. 1, 2. 



Transversely ovate, inflated, thickness equal to balf its 

 breadth ; umbones produced, rounded, and contiguous ; pos- 

 terior side short and obliquely truncated ; anterior side long 

 and sub-truncated ; hinge-line almost parallel ; external sur- 

 face with a few remote concentric wrinkles or lines of growth. 



I found this species in the Coal Shale at Dalkeith, Mid- Lothian. 

 Named in honour of my v.ilued friend, James Gerard, Esq., Retreat, 

 East Lothian. 



2. Unio latekalis. — The Broad Unio, pi. LXXIII. f. 20. 

 Pachi/odon lateralis. Brown, Ann. Nat. Hist. Dec. 1843, 



pi. 15. tig. 3. 



Transversely elongated, sub-quadrate, cuueifonu ; sides very 

 unequal, the anterior one very long, gradually sloping from 

 the umbones, and terminating in an obliquely truncated point ; 

 posterior one very short ; umbones produced, with acute but 

 not inflected beaks. Length somewhat more than half an 

 inch ; breadth nearly an inch and a-half. 



lu the Coal Shale, Whitehaven. 



3. Umo sulcatcs. — The Furrowed Unio, pi. LXXIII. 

 figs. 28, 29. 



Pachyodon sulcatus. Brown, Ann. Nat. Hist. Dec. 1843, 

 pi. 15, figs. 4, 5. 



Sub-triangular, rather compressed ; umbones prominent, very 

 close, slightly reflected, sub-acute, and placed considerably to 

 one side ; general surface smooth, with inequidistant concen- 

 tric furrows ; posterior side arcuated, with a rounded point situ- 

 ate low ; anterior side gently rounded ; basal line nearly paral- 

 lel. Lensrth ime and a-h:ilf inch ; thickness one half iuch. 



The Shale near Whitehaven. 



This species is liable to some variety in external contour. 



4. U.Nio RUGOsus. — The Rugged Unio, pi. LXXIII. figs. 

 14, 15. 



Pachyodon rugosus. Brown, Anu. Nat. Hist. Dec. 1843, 

 pi. 15, figs. R, 7. 



Sub-triangular, greatly ventricose in proportion to its size, 

 its depth being equal to five-sixths of its whole length ; um- 

 bones verv prominent, situate considerably to one side, point- 

 ing posteriorly, and remote from each other ; anterior side ab- 

 ruptly descending and rounded ; posterior side gradually slop- 

 ing and considerably more acute than the other ; ligament 

 produced ; external surface with unequal, rugose, concentric 

 wrinkles. Length two inches five-eighths ; breadth three 

 inches and a-half ; thickness two inches and a quarter. 



The young shells are much more rugosely wrinkled than the 

 adult. 



Found in the Ironstone Shale at Sheden, by Mr S. Gibson of 

 Hebden Bridge, and in his cabinet. 



5. Uxio suB-ROTCNDUS. — The Sub-rotund Unio, pi. 

 LXXIII. fig. 22. 



Pachyodon sub-rotundus. Brown, Ann. Nat. Ilist. Dec. 



1843, pi. 15, fig. 8. 



Sub-rotund ; umbones sub-central, produced, blunt, and 

 somewhat remote from each other ; hinge-line considerably 

 arcuated ; surface with irregular, acute, concentric wrinkles ; 

 thickness about equal to half its lengtli. 



The Coal Shale, Oldbara. 



G. U.vio iiiPENNis. — Two-winged Unio, pi. LXXIII. f. 27. 



Pachyodon bipennis. Brown, Ann. Nat. Hist. Dec. 1843, 

 pi. 15, fig. 9. 



Transversely elongated, somewhat hatchet- .■shaped ; sides 

 unequal ; umbones produced and remote ; hinge and basal 

 lines nearly parallel ; anterior side short and roun<led ; poste- 

 rior side elongate, and obliquely sub-truncate from the hinge- 

 line, terminating below in a short, slightly acuminated curve ; 

 surface rather smooth, with a few distant, transverse, shallow 

 grooves. 



The Ironstone Shale at Low Moore, Yorkshire. 



7. Unio Dawsoni. — Dawson's Unio, pi. LXXIII. fig. 3. 

 Pachyodon Dawsoni. Brown, Ann. Nat. Hist. Dec. 1843, 



pi. 15, fig. 10. 



Orbicular ; umbones central, large, produced and remote ; 

 surface nearly smooth, with onlv a few nearly obsolete concen- 

 tric wrinkles ; thickness equal to more than half its diameter. 



Found in the Ironstone Shale at Low Moore, near Bradford, 

 and is in the Cabinet of Mr S. Gibson, and named in honour 

 of Miss Dawson of Low Moore, an accomplished geologist. 



8. Unio nanus. — The Little-vessel Unio, pi. LXXIII. f. 7. 

 Pachyodon nanus. Brown, Ann. Nat. Hist. Dec. 1843, pi. 



IG, fig.'l. 



Smooth, posterior side elongated, and obliquely sub-truncate 

 above; sub-acute above ; anterior side rounded ; umbones pro- 

 duced and rounded ; hinge-line arcuated. 



Coal Shale at Middleton, near Leeds. 



9. Unio Rhindii. — Rhind's Unio, pi. LXXIII. fig. 5. 

 Pachyodon Rhindii. Brown, Ann. Nat. Hist. Dec. 1843, 



pi. IG, fig. 2. 



Sub-acute at both extremities ; basal line considerably arcu- 

 ated, rather produced opposite the umbones ; posterior side 

 turned slightly upwards; umbones sub-central, rather pro- 

 duced, and very close ; hinge-line curved ; surface with trans- 

 verse, shallow, irregular wrinkles. Length equal to two-thirds 

 of its breadth. 



In the Coal Shale, Polmont, Stirlingshire, by my friend 

 William Rhind, Esq., author of "The Age of the Earth," &c. 



10. Unio amygdala. — The Almond Unio, pi. LXXIII. 

 fig. 4. 



Pachyodon amygdala. Brown, Ann. Nat. Hist. Dec. 1843, 

 pi. 10, fi-. 3. 



Inflated, anterior side rounded ; posterior side acuminated, 

 with an acute beak-like termination ; umbones rather obtuse 

 and remote ; basal line considerably arcuated ; surface with 

 manv irregidar acute wrinkles. 



Ironstone Shale, Low Moore, Yorkshire. 



11. Unio exoletus. — The AVorn Unio, pi. LXXIII. f. 25. 

 Pachyodtm exoletus. Brown, Add. Nat. Hist. Dec. 1843, 



pi. 10, fig. 4. 



Shell transversely elongate, its breadth about double its 

 length ; surface quite smooth ; umbones blunt, placed near to 

 the anterior side, which is round ; posterior side acuminated 

 anil sub-acute ; hinge-line slightly arcuated ; basal line nearly 

 jiarallel ; thickness somewhat more than half its length. 



Ironstone Shale, Low .Moore, near Bradford. 



12. Unio dubius. — 'i'he Doubtful Unio, pi LXXIII. f. 13. 

 Pachyodon dubius. Brown, Ann. Nat. Hist. Dec. 1843, 



phlG, fig. 5. 



Sub-ovate, both sides rounded ; umbones slightly produced 

 2 R 



