30 



cotkle form, but im'menfely large; area, fliells formed 

 Jike an ark; ollrea, the eicallop, common oyfter, &c. 

 aiiomia, the beaked cockle; mytilus, the mufcle ; pinna, 

 the fea-wiiig or ham. He alfo very accurately delcribcs 

 the Angular habits- and curious economy of many of thefe 

 (hcll-tilli, whicli iee under their refpeiftivc names in this 

 work. 



Dr. Woodward, in his catalogue of foffils, has given a 

 very good method of bivalves, on the charafler of the 

 hinges, and alio on the form ; but his fyftem of univalves 

 is very faulty and imperfefl. The technical terms com- 

 monly ufed for defcribing the parts of bivalves, and 

 wliich are requifite for making their defcriptions intelli- 

 gible, are as follow : The (ummit, (apex,) r-. the part 

 whereon the teeth, joints, or properly the hinges, are 

 placed. The beaks, (umbones,) are the peaked ends of 

 the (hell, which nioft generally ftand behind the fummit, 

 or that part which anfwers to it. The margins, or bor- 

 ders, (iiuii-giiies,) are the edges or contour of the ihell, 

 produced from the beak or hinge on either fide. The 

 lurfaces, (fuperficks,) concavitas & convexitas concha- 

 rum ; the convex exprtffes the exteiior-or convex liile of 

 the (hells, ami the concave, the infide. The Uugtb of a 

 bivalve is from the beak or hinge to the very oppofite 

 extreme. The breadth is from fide to fide. The margins 

 or borders are faid to he Jmilar, if equally juoduced or 

 extended from the fumniit, or of equal length ; and itijji- 

 milar, if unequal or rnore extended on one fide than on 

 the other. The hinge, (cardo,) is the part that connefts 

 the two valves together, that is to fay, thejoints on wdiich 

 they play in the aiilions of opening and (liutting. A hinge 

 is (aid to be inarticulate, when not fet with any vifible 

 joints or teeth ; articulate, when fet with fome few; mult- 

 articulate, wlien fet with many, or a large number. The 

 furrow, (/ulcus canaliculus,) is the gutter or furrow, when 

 the (hells are^ doled, that is extended, or runs along paral- 

 lel to the hinge. The (lopes, (ctecU'vitas,) are the places 

 which dope or flant from the beak down the fides, and 

 generally are fiightly flatted, fliallow, or concave. The 

 vent, (ri»ia,) is the opening of the (hells on the flopes. 

 The cartilage, (cartilago,) joins the valves together at 

 the furrow and at the (lopes. The flat, (pleiiiities, latus 

 . complanatum,) is that fide of thofe (hells that is flat; as 

 the flats of the heart cockles, bears paws, &.'C. 



BIVALVES WITH UNEQUAL VALVES. 



Thefe confift of fliells that have irregular valves, and 

 • fliut clofe. The firft family confifts of the peftens, or 

 efcallops. Though fome fpecies of them have equal 

 valves, yet, as the far. greater number have unequal 

 ■valves, viz. a flat and a concave fide, they are ranged un- 

 der this genera! head. The fame particular likewife occurs 

 in the families of the fpondyles and ovlters. 



ESCALLOP.— The ellential charaiUr of the efcallop 

 family, is a trigonal finu,s, and an claftic cartilage for its 

 hinge in the very center of the top of the (liell. The fub- 

 crdinate charafters of efcallops are their being eared ; in- 

 deed mofl: authors have injudicioufiy made it the chief 

 tharaiiter, wdiereas there are other eared fliells befides 

 efcallops, as the fpondyles, raargaritiferse, &c. and, -vice 

 ijer/a, there may be efcallops without tars. The other 

 Jubordinate character is to have the top run into a per- 

 feel (trait line, and thence gradually widen to a round 

 bottom. The fpecies are numerous, foine whereof are 

 very curious, and of great beauty, as the ducal mantle, 

 the com pals or fole, the duck's foot or coral-efcallop, &.'c. 



It is worthy of remark, that the colours of the under 

 fliells of efcallops are always fainter than the colouis of 

 the upper fliells, and fometinies the valves are diflerently 

 coloured, as the compafs or (ble, which has one valve of 

 a chefnut brown, the other valve inilk white. Moll au- 

 thors rank thefe fliells as apaiticular family, and call 

 them pefte'ns. Gualteri makes dlflisrent genera of thofe 

 with equal, an<l thofe with unequal, valves ; the former 

 J'.e calls peclen, the latter concha peiSlinata; and the elcal- 



CONCHOLOGY. 



lops with unequal or (ingle cars, he calls pefluncuH. Liii- 

 na;us makes them a genus of oyllers, and has accordingly 

 arranged them under the generic name Ostrea. It is 

 faid, that efcallops will move fo ftrongly as fometimes 

 to leap out of the balket wherein they are placed when 

 taken: their mode of leaping, or raifmg themfelves up, 

 is by forcing their under valve againlt the body wdiereon 

 they lie. 



The chief kinds of folTiI efcallops yet in an undifco- 

 vered (Kate, are as follow : The firli is about the fize of 

 the common oylter, with large but unequal ears, of, a 

 perfei^^ly round contour ; the furface tranfverfely thick 

 let with prominent fliarp thin ridges, like plates. The 

 valves are equal. Thele are found very frequently in the 

 quarries at Thame in Oxfordlhire. A fecond kind, very 

 elegant, is about double the fize of a cockle, the valves 

 unequal, one being quite flat, the other exceedingly con- 

 cave. It is thickly ridged lengthways, with many com- 

 mon ridges and intermediate ones, that are very promi- 

 nent or high, and the furrows are broad and deep. It is 

 found in the quarries of Dorfetfliire, Wiltlhire, and the 

 adjacent counties; and Ibmetimes in the chalk-pits of 

 Kent and Surrey. 



SPONDYLE. — The fecond family in this divifion is 

 the fpondyli. The fpondyles are mofl: generally eared 

 (hells with unequal valves, rude or uncouth in fliape, par- 

 taking of the ruggednefs of the oyfi;er, with fomewhat of 

 the efcallop form, (b as to produce a medium between 

 the two families. However, the fpondyles, like the efcal- 

 lops, have (bme fpecies with equal valves, and without 

 ears. The efl'ential charadler is the hinge, which in the 

 upper fiiell confills of a triangular hollow and cartilage, 

 like the efcallop, in the very center; on each fide of 

 wdiich is a large deep cavity, and a very large thick and 

 prominent tooth or joint lies on each fide of the cavity. 

 The (limmit and beak of the under valve is alfo extremely 

 thick and (frong, and extends from the hinge outwards 

 into a broad triangular flope or flat. 



Some kinds of fpondyles are thickly and curioufly fet 

 with long thorns or (pikes; thefe are generally called 

 thorny oyjlers, and, wdien perfeft, are greatly valued. This 

 family is not very numerous in its fpecies. Lilter, Wood- 

 ward, Gualtieri, Linnaeus, and Meufchen, all rank them 

 as a particular genus, by the name of fpondylus ; but 

 Rumphius, Argenville, and Davila, rank them very er- 

 roneoufly as oyfters. 



OYSTER. — The third family in this divifion is the of- 

 treum, or oyfter. The oyfters have unequal valves, though 

 there are fome fpecies that have equal valves, but none are 

 eared. The hinge of this family has not any teeth, but 

 confiifs of one large inarticulate gutter running the length 

 of the top of the fliell, in both fliells alike, and is covered 

 and filled with a llrong cartil.age. The fpecies are very 

 numerous; (bme of which are curious, though not beau- 

 tiful, and bear a large price, as the hammer oyfter, the 

 cockfcombs, &c. This family is ranked as a diilindl one 

 by all authors, but with many additions or omiflions : as 

 for example, Linnaeus ranks the efcallops with them, and 

 Argenville and others the fpondyles, while Lilter ranks 

 the hammer oyflier, and (bme others, as efcallops. 



It is not uncommon to fee on oyfter-fhells, when in a 

 dark place, a fliining matter or bluifti light like phofpho- 

 rus, which (ticks to the fingers when touched, and conti- 

 nues fliining and giving light far a confiderable time, 

 though without any fenfible heat. This (billing matter 

 being fubje6led to the microfcope, is found to confilt of 

 three kinds of animalcules ; the firft whitifh, and having 

 twenty-four or twenty-five legs on a fide, forked, and a 

 black I'peck on the head, the back like an eel with its (kin 

 (tripped oft'. The fecond Ibrt is red, refembling the com- 

 mon glow-worm, with folds on its back, and legs like 

 the former, a nofe like a dog, and one eye in front of 

 the head. The third kind is fpeckled, with a head like a 

 (ble, with many tufts of whitifli hairs on the fides of it. 

 The foflil oylters yet undilcovercd in a recejit or living 



itate. 



