ORGANIC REMAINS. 



339 



ged ; transversely furrowed, and the lines of growth strongly 

 marked; anterior lobe somewhat angular, and pointed ; poste- 

 rior lobe smaller, and rounded. 1'ound at Toddenham, near 

 Shipston-on-Stour. 



Cardita planicostat a. F. 127. With about twenty, longitu- 

 dinal, divergent, flat, broad ribs, and the interstices very nar- 

 row; muscular impressions large and deep; margins strongly 

 crenulated. 



Cardita ajar. F. 126. Subcordiite, with compressed longi- 

 tudinal angular ribs, and the furrows subtuberculate ; anal 

 depression round. 



I'enits lineolata. F. 136. Somewhat gibbous, and cordiforra ; 

 partly covered with zigzag striiB ; anterior side smooth ; edge 

 entire; beak rather prominent; cicatrix slightly defined and 

 cordate. Found at Blackdown, near Collumpton, Devonshire. 



Cytheria exoleta. F. 123. Orbicular, finely striated concen- 

 trically; and with the lines of growth well defined; beaks 

 prominent ; lunale heart-shaped, and pointed. 



MYACONCHA. Equivalve, sides oblique, very unequal ; hinge 

 with an elongated oblique tooth in the left valve, and provided 

 with an external ligament ; beaks placed close to the posterior 

 extremity, destitute of a sinus in the impression of the mantle. 



Myaconcha crasia. F. 146. Ovate, mytiliform, thick-pointed 

 at one end, and obtuse at the other, convex very slightly 

 wrinkled ; ligament placed in a wide and deep groove, length 

 double its breadth. Found at Dundry, near Bristol, in the 

 ironshot oolite. 



Crassina lurida. F. 134. Transversely oblong, depressed, 

 with numerous transverse, indistinct ribs ; lunette elliptical, 

 sharp; margin crenulated internally. Found in blue sandy 

 clay, Foxhill quarries, Gloucestershire. 



THETIS. Equivalve, subequilateral, more or less orbicular, 

 and very convex ; ligament marginal ; hinge with three or four 

 accumulated teeth ; the line of attachment of the mantle, with 

 a deep sinus extending nearly to the beak ; muscular impres- 

 sions orbicular, small, and remote from the hinge; ligament 

 internal. 



Thetis minor. F. 148. Gibbous, wider than long; posterior 

 edge rounded. Found in the green sand, Parham-Park, Sus- 

 sex. 



Petricoli laminosa. F. 141 . Ovate, gibbous, with erect con. 

 centric lamina: ; posterior side subcuneiform ; a single broad 

 bifid tooth in the left valve, and two small teeth in the other. 

 Found in the Suffolk cratr. 



Lutraria gibbosa. F. 131. Gibbous, anterior side much wider 

 than the posterior, recurved, truncated', and gaping ; length and 

 depth equal ; beaks much incurved and pointed. Found in the 

 oolite limestone, Bath. 



Mya mandibula. F. 124. Gibbous, depressed in the middle, 

 transversely undulated ; anterior side square, gaping, aperture 

 oblong ; posterior side somewhat straight ; depth two- thirds its 

 length; beaks incurved and pointed. Found in Micaceous 

 sandstone at Devizes, Wiltshire. 



PHOLADOMYA. Transverse, thin, snbhyaline, ventricose ; the 

 anterior portion short, rounded, the posterior more or less 

 angulated and gaping ; hinge composed of an elongated subtri- 

 gonal foveola, and a marginal plate in each valve ; ligament, 

 external, rather short ; two indistinct muscular impressions ; 

 sinus in the impression of the mantle large ; umbones approxi- 

 mated. 



1'holadomya murchisoni. F. 150. Ovate, beaks very large ; 

 anterior side short, with six or seven elevated, obtuse, knotted, 

 divergent ribs, occupying the middle area of the valves. Found 

 at Brora, Sutherlandshire. 



Teredo antenautce. F. 167. Valves transversely striated ; 

 the anterior side with numerous, smooth, striae ; dorsal and 

 posterior accessory valves shelly. Found in Essex. 



CLASS VII. CIRRIPEDA. 

 ORDER I PEDUNCULATA. 



Pollicipet sulcatus. F. 168. Valves with longitudinal, ele- 

 vated striae, the central valve elongated, rhomboidal ; posterior 

 valve arched, broad lanceolate, and subcarinated, both marked 

 with irregular, elevated, longitudinal striae. Found in the 

 upper chalk at Norwich. 



ORDER II SESSILIA. 



Balanus tetselatui. F. 53. Obliquely conical, thin, with 

 six indistinctly ribbed valves, smooth; interstices transversely 

 striated, producing a tesselated appearance; aperture oval. 

 Found at Bramerton, Norfolk. 



CLASS VIII. ANNELIDES. 



Serpula crassa. F. 1R9. Acutely conical, round within, 

 triangular externally, about four times as large as the diame- 

 ter of the end at the aperture. Found at Highgate. 



fSpirorbi* concnmu. F. 51. Discoidal, involute, concave on 

 one side ; the last volution but slightly attached. Found in the 

 green sand at Dillon, near Wectbury. 



Dentalium nitew. F. 74. Slightly incurved, gently taper- 

 ing to the smaller end ; surface smooth and shining ; aperture 

 circular. Found in clay at Highgate. 



The total number of species of fossil shells, which have hitherto 

 been discovered in the tertiary series, is 3036. Of these, there 

 are found in the Eocene period of strata, 1238 species; in the 

 Miocene, 1021 ; in the older and newer Pliocene divisions, 777. 

 In the newer Pliocene period, there are from 90 to 95 per cent, 

 of recent species ; in the older Pliocene period, from 35 to 50 

 per cent.; in the Miocene period, 18 per cent.; and in the 

 Koceue, 3| per cent. 



The following species of shells are peculiar to the PLIOCENE 

 TF.BTIARV PERIOD, and figured in pi. LXVI. Turbo rugosus, 

 f. 106; Trochus Magus, f. 97; Solarium VariegHtum, I. 10.); 

 Tornatella fasciata, f. 9a; Pleurotoina Vulpecula, f. 103; P. ro- 

 l 1;i, I. 92; Fusus crispus, f. 102; Jim-cumin prismaticum, f. 

 104; B. Semistriatum, f. 94; Mitra plicatula, f . 93 ; Cassidaria 

 echinophora, f. 90; Cytherea exoleta, f. 123. 



MIOCENE TERTIARY PFRIOD. 



Voluta rarispina, f. 87 ; Mitra Dufreuei, f. 101; Pleurotoma 

 denticula, f. 107; P. tuberculosa, f. 86; Nerita Plutonis, f. 91 ; 

 Turitella proto, f. 90; Fasciolaria turbiuelloides, f. 9'J , Carditii 

 ajar, f. 126. 



EOCENE TERTIARY PERIOD. 



Voluta costaria, f. 108; Pleurotoma clavicularis, f. 84; Cas- 

 sidaria carinata, f. 85 ; Nerita tricarinata, f. 83 ; Calytraea trochi- 

 formis, f. 89; Turitella imbricataria, f. 88; Voluta digitalina, 

 f. 98; Natica epiglottina, f. 100; Solarium canuliculatuin, f. 82. 

 Cardita planicostata, f. 127; Quinquelocnliua Striatula, f. 110; 

 Clavulina corrugata, f. 112. 



To illustrate the variety which exists among these 

 fossils, and, at the same time, to give an idea of the 

 manner in which they disagree with recent shells, we 

 shall give the results of the examination of British 

 fossil shells. The number of genera at present known 

 to British naturalists is about 140, which comprise 

 nearly 3000 species. Of these 



Species. 



58 genera are simple univalves, which comprise 40fi 

 62 simple bivalves, . . . 590 



3 complicated bivalves, . . 51 



12 multilocular bivalves, . . 240 



To ascertain the relative proportion of the different 

 classes contained in strata of different periods, we 

 make three principal divisions in the formations con- 

 taining organic remains : the first is the most ancient 

 series ; the second or middle division contains the 

 remainder of the secondary strata; and the third 

 consists of the tertiary deposits. The first, which is 

 the lowest or most ancient division, may be sub- 

 divided into two series of formation : 



1. Carboniferous order of Mr Conybeare. 



Speciet. 



Simple univalves, . . . . .27 



Simple bivalves, ..... 34 



Complicated bivalves, 

 Multilocular univalves, . 



140 



2. From the carboniferous to the lias inclusive. 



Species. 



Simple univalves, ..... 9 

 Simple bivalves, . . 33 



Complicated bivalves, . - 5 



Multilocular univalves, . . 50 



97 



The second or middle division, from the lias up- 

 wards, includes the entire oolitic series, and the 

 strata up to the chalk inclusive :- 



Spectei. 

 106 



Simple univalves, . 

 Simple bivalves, 

 Complicated bivalves, 

 Multilocular univalves, 



139 

 620 



The third, or most recent division, comprises all the 

 beds above the chalk, or the tertiary formations : 



Simple univalves, . 

 Simple bivalves, 

 Complicated bivalves, 

 Multilocular univalves, 



ftpeciet. 

 259 

 141 







8 



406 



The shells of the most ancient formations exceed, in 

 complexity of structure, those in the subsequent 

 strata, and in our present seas. They are more fre- 

 quently endowed with that complicated structure 

 which enabled their inhabitants to rise and sink with 

 them in the water. Of this class are the numerous 

 race of many-chambered univalves the nautilites, 

 the ammonites, and orthoceratites ; and of the class 

 of complicated bivalves are the spirifers, and the 

 j genera peritameras and productus. The table given 

 .Y 2 



