Pin 



CONCHIFERA. 



169 



riglit haiul valve tliaii in tlie opposite ; the interior pearlaceous 

 substance of the shell is spread out almost in the same form as 

 the exterior fibrous and more extended portion ; one distinct, 

 somewhat obliijuc and irregular muscular impression, and a 

 series of small dots, are placed at the posterior side, near the 

 sinus for the byssus, which answer as points of attachment for 

 a part of the mantle. 



1. Pekna al.eformis. — The Wing-shaped Perna, pi. 

 LXXI. lig. 20. 



Modiola (?) alw/onnis. Sowerby III. p. 93, pi. 251. 



Triangular ; length neaxly twice its breadth, producing a 

 wing-like appearance; rentricose; anterior lobe somewhat 

 compressed ; posterior lobe very small ; back parallel ; disk 

 convex ; beaks produced, between one and the other a con- 

 cave space intervenes ; surface rough and somewhat imbricat- 

 ed ; thickness of the united valves equal to the width of the 

 shell. 



The Lower Greensand, Court- al-Strect. 



2. Perx.4 mytiloides. — The Mytilus-formed Perna, pi. 

 LXVII. figs. 1, 2. 



P. mvti/oitk.^. Phillips, Geo. York, I. pi. 9, fig. 21. 



Mytiliform, elongated ; posteriorly incurved ; hinge-line 

 slightly curved and considerably oblique ; ligamentary grooves, 

 seven or eight, elongated ; beaks rather obtuse, pointing pos- 

 teriorly ; surface smooth, with shallow, concentric lines of 

 growth. 



The Combrash, Bullwick ; the Great Oolite, White Nab, 

 Cloughton Wyke, and the Inferior Oolite, Cheltenham. 



S. Per.n.v quadrata. — The Squarish Perna, pi. LXIX. 

 fig. 11. 



P. qiHidraki. Sowerby, V. p. l-i.9, pi. 492. 



Elongated, somewhat square ; valves with one side shorter 

 than the other, gibbose and unequal ; hinge-line a little 

 curved ; the cartilage pits large and few ; beak rather pointed, 

 that of the larger valve prominent, the other somewhat shorter ; 

 surface smooth, with a few indistinct, shallow lines of growth. 



The Portlaml Stone, Swindon and Garsington. 



4. Perna rostkata. — The Beaked Perna, pi. LXIX. figs. 

 14. 15. 



P. rostrala. Sowerby, Geo. Tr. 2d Ser. IV. p. 342, pi. 17, 

 fig. 17. 



Ovate, compressed ; hinge-line straight and horizontal ; 

 lesser wing produced and well defined ; base rounded ; beaks 

 rather obtuse and not protruding ; substance of the shell thin. 



In the Greensand, Blackdown. 



.5. Perna ruoosa. — The Rugged Perna, pi. LXI.*** f. 3. 



P. ruffosa. Goldfuss, pi. 108, fig. 2. 



Sub-quadrate; hinge-line lengthened, oblique; area with 

 eighteen or nineteen oblong parallel grooves ; beaks acute, con- 

 siderably turned to one side, with a lunular excavation under 

 them ; surface with many irregular, raised, concentric rough 

 lines of growth. 



The Great Oolite, Scarborough. 



Tribe II.— MYTILACEA. 



Hinge with the ligament sub-anterior, marginal, linear, 

 very entire, occupying a great portion of the anterior bor- 

 der ; shell rather foliaceous. 



Genus XXXII.— PINNA.— iy««»«>M. 



Shell equivalve, longitudinal, oblique, wedge-shaped ; beaks 

 forming an elongated point ; posterior side generally trun- 

 cated, and always gaping ; the anterior margin nearly a 

 straight line, and a little open in the centre for the passage 

 of the byssus ; hinge without teeth ; ligament margin greatly 

 lengthened and linear; ligament partly internal, and continu- 

 ing along the whole dorsal margin ; two muscular im- 

 pressions in each valve, the posterior one very large, almost 

 central, the anterior one terminal, and sometimes double ; 

 muscular impressions of the mantle destitute of a sinus. 



1. Pinna ampla. — The Spacious Pinna, pi. LXXI. 

 fig. 19. 



Mi/dliis arnpliii. Sowerby, I. p. 27, pi. 7. 



Triangular, compressed ; posterior side straight, slightly 

 undulous ; base gradually curved to the back ; length 

 nearly twice its breadth, somewhat compressed ; surface with 

 rather wide, longitudinal, undulating stria;, which proceed from 

 the beaks and back near to the base, the posterior side not 

 striated ; substance of the shell thin. 



The Great Oolite, Bath and Malton, and the Inferior 

 Oolite, Somersetshire and Yorkshire. 



2. Pinna flabelliformis. — The Fan-shaped Pinna, pi. 

 LXVII. fig. 19. 



P. costata. Phillips, Geo. York, II. p. 211, pi. 0', fig. 2. 



Much elongated, narrow, nearly straight ; beaks acute, mid- 

 dle of the valves with many longitudinal, narrow, deep 

 grooves, crossed by remote, concentric lines of growth ; to- 

 wards the beaks the valves are destitute of grooves. 



The Carboniferous Limestone, Ashford, Bakewell, Bo- 

 land and Moulton. 



3. Pinna gracilis. — The Slender Pinna, pi. LXIX. 

 fig. 12. 



P. ffracilis. Phillips, Geo. York, I. pi. 2, fig. 22. 



Much elongated, slender, slightly arcuated ; beaks rather 

 obtuse ; anterior side with longitudinal shallow furrows ; 

 and remote, shallow, transverse lines of growth. 



The Specten Clay, Speeton, Yorkshire. 



4. Pinna lanceolata. — The Spear-shaped Pinna, pi. 

 LXIX. fig. 10. 



P. lanceolata. Sowerby, III. p. 145, pi. 281. 



Lanceolate, much elongated, its length being equal to four 

 times its breadth ; and a little arcuated, section quadran- 

 gular ; each valve being divided into two flat sub-triangular 

 parts by a mesial line ; surface with some longitudinal wide- 

 set strim at the beaks, and extending downwards for some 

 inches, with transverse, shallow wrinkles. 



The Ciiral Rag, Scarborough, Malton, and ^lagilligan, 

 Ireland. 



5. Pinna inflata. — The Inflated Pinna, pi. LXVII. 

 fig. 12. 



P. inflata. Phillips, Geo. York, II. p. 21 1, pi. 6, fig. 1. 

 Conical, inflated ; beaks nearly central ; surface with many 

 small, close-set, equal furrows. 



The Carboniferous Limestone, Bolland, Yorkshire. 



6. Pinna cdneata. — The Wedge-shaped Pinna, pi. LXIX. 

 fig. 13. 



P. cuneata. Phillips, Geo. York, I. pi. 9, fig. 17. 



2<i 



