TESTACEOUS FISH. 



337 



ilso found eaten through, either by worms, 

 or by each other ; and they are thus rendered 

 less valuable ; but what decreases their price 

 still more is, when they are scaled and worn 



Involuted spire. Those univalve shells which have 

 their volutions concealed inside of the body of the shell, 

 as in the Nautili and Cypraea, pi. 33. fig. 70. 



Reversed or Heterostrophe spire, is when the volutions 

 of the spire revolve in a contrary direction to that of a 

 common screw; in which case the aperture is on the 

 right side, in place of the left, which is the case with 

 all dextral shells, pi. 33. fig. 71. 



Detaclied spire, is when the volutions are not adhering 

 together at their base, pi. 33. fig. 67. 



Suture of the spire a fine thread-like line, which runs 

 spirally between the volutions, pi. 33. fig. 65 f, f,f,f\f. 



Sides, are the extreme edges of the shell, when the 

 back or front is held next the observer, d, d. 



Chamfers, are the intervals, between the partitions or 

 septa, of multilocular shells, pi. 33. fig. 6866, &c., and 

 also occur in simple univalves, f. 73. 



Siphuncle is the tube which extends through some of 

 the multilocular univalves, pi. 33. fig. 68 a. 



Septa, are partitions which divide the chambers in 

 multilocular shells, f. 68 c, c, &c. 



Varices, are transverse ribs which cross the volutions 

 in some species of Murex, Triton, Buccinum, Cassis, 

 &c., f. 69 aa. 



Ribs, longitudinal and transverse projections, f. 75 a 

 a; an example of the former; those in f. 74 illustrate 

 the latter. 



Teeth, some projecting laminae in the aperture of uni- 

 valves as represented in the aperture of pi. 33. fig. 71. 



Umbilicus, a perforation in the base of the body of 

 Helices, Trochi, &c., pi. 33. fig. 76* a. 



PARTS OP BIVALVES. 



Equilateral Shells, are those whose sides are alike, that 

 is, both of a uniform size and shape, pi. 33, fig. 85. 



Inequilateral Shells, have unequal sides, and of differ- 

 ent shapes, as in Donox Lutraria, &c., pi. 33, fig. 77. 



Summit, is the most elevated part of the shell, in which 

 the hinge is usually situated, pi. 33, fig. 77 a. 

 __Base, the opposite extremity of the above, pi. 33, fig. 

 77 o. 



Anterior slope, is that side of the shell in which the 

 ligament is. situated, pi. 33, fig. 77 d. 



Posterior slope. The opposite of the above, and may 

 be distinguished by viewing the shell in front, when the 

 beaks point to the observer, pi. 33, fig. 77 -e. 



Disk, the most prominent part of a valve, if lying with 

 its inside undermost. 



Cicatrix, the internal impression by which the animal 

 was aflixed to the shell, pi. 33, fig. 1lgg,f 80; d,L 81 

 e. 



Lunule, the crescent-shaped depressions, in the pos- 

 terior and anterior slopes, pi. 33, fig. 77 h, 



Ligament perforation, the circular aperture through 

 which the ligament passes, as exemplified in the Ano- 

 mise, pi. 33, fig. 82 a. 



Hinge, that part by which the shells are united. It 

 is generally constructed of teeth ; those of the one valve 

 fitting into a socket in the opposite one. Some shells 

 have no teeth, but are merely kept together by the li- 

 gament, in which case they are called inarticulate-, when 

 they have many teeth, they are called multiartieulate. 

 The Hinge is that part which affords the most promi- 

 nent generic distinction in bivalves. 



Teeth of the hinge. The number, relative situation, and 

 construction of these, afford the best specific distinc- 

 tions in bivalves. A spatuliform central tooth is exhi- 

 bited, pi. 33, fig. 78. 



Primary teeth, are those situated in the centre of the 

 hinge. They are also termed the cardinal teeth, pi. 33, 

 "g. 77 i. 



Lateral teeth, are those divergent from the umbo; are 

 usually long, flat, and frequently double, or divided by 

 a groove, pi. 33. fig. 80 a a. 



Double teeth. When teeth are very deeply cleft they 

 are so termed. 



by lying too long empty at the bottom, or ex- 

 posed upon the shore. Upon the whole, how- 

 ever, sea-shells exceed either land or fossil- 

 shells in beauty; they receive the highest 



Incurved teeth, are those which are bent round, as in 

 the Spondylus Gsederopus, Solen Siliqua, &c., pi. 33. fig. 

 79. c. 



Recurved teeth, such teeth as are bent backwards are 

 so termed, as in the hinge of the Panopea Aldrovandi, 

 pi. 33. fig. 11 ;f. 81 a a. 



Numerous teeth, are generally set in rows, either 

 straight or curved as in pi. 32. fig. 37, 38, 39. 



Cavity of the hinge, is a pit or hollow in which the li- 

 gament is inserted in the Ostrea, &c., as may be seen in 

 pi. 32. fig. 20. 



Ligament, is that cartilaginous substance by which 

 the valves are held together, and is situated under the 

 hinge of the shell, pi. 33. fig. 77 k ; f. 806. The ca- 

 vity in which it is inserted, f. 81 6; f. 83 6. 



Beak, the extreme point or summit of bivalves, which, 

 for the most part, is turned aside, or downwards, so 

 that it is seldom the highest part of the bivalve. 



Umbo, that part situated immediately under the 

 beak, pi. 33. fig. 84 a. 



Ears or Auricles, are those processes, situated on one 

 or both sides of the beak, as in the scallops, pi. 33. fig. 

 81' c c. Superior ear, 85 a. Inferior ear, b. 



Margin, the extreme edges of the entire shell. 



Crenulated margin. When the margin is notched as 

 in the common edible cockle it is so termed, pi. 33. fig. 

 80 cc. 



Strice, are fine thread-like lines, which traverse the 

 exterior surface of shells, as exemplified, pi. 32. fig. 62, 

 63. 



Spines, are exterior acutely pointed protrusions, com- 

 posed of shelly matter, pi. 33. fig. 81 d d. 



Right valve, may be distinguished by the anterior 

 slope, pointing to the right hand, when the valve is 

 viewed with the inside uppermost, pi. 32. fig. 46 the 

 under valve, in many species, is flattened, as in the os- 

 trea. 



Left valve, the opposite of the above, or where the an- 

 terior slope points to the left hand, pi. 32. fig. 46. 



Length of the shell is always understood to be from 

 that part in which the ligament is situated to the oppo- 

 site extremity. Bivalve shells are called longitudinal, 

 when their greatest length is from the hinge to the op- 

 posite margin, pi. 33. fig. 80 and 85, from a to 6 ; 

 and transverse, when their breadth exceeds their length 

 fig. 77 from c to c; and fig. 79 from a to a. 



Byssus, or beard. An accessory filamentary appen- 

 dage of a silky texture, by which some bivalve shells are 

 affixed to rocks, stones, &c. as may be instanced>in the 

 common muscle. Sides the right and left parts of the 

 valves ; pi. 33. fig. 77 c, c. 



Ribs are longitudinal or transverse protuberances, ge- 

 nerally running parallel to each other on the external 

 surface of bivalves. Longitudinal ribs, pi. 33. fig. 83 a. 

 Transverse ribs, f. 84. 



Accessory valves are small, unattached valves in the 

 genus Pholas, pi. 33. fig. 86. a. 



Valves of Chitons are placed transversely along the 

 back of the animal, usually eight in number, pi. 33. fig. 

 90 a, a, &c. Fig. 91, a central valve ; 92, a terminat- 

 ing valve. 



Margin in Chitons, is a fleshy border which surrounds 

 the valves, pi. 33. fig. 906. 



PARTS OF CIRRIPEDES. MULTIVALVES. 



Opercuhim consists of from two to four small valves, 

 placed in the opening at top of the Balani, pi. 33. fig. 



Base the part by which the shells of the genus Ba- 

 lanus, &c. are attached to rocks, pi. 33. fig. 87 e; f. 88 

 6. 



Ligament a membranous substance, by which the 

 valves are attached, pi. 33. fig. %1d. 



Ridges are convexities in the Balani, &c., sometimes 

 longitudinal and at others transverse. 



