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EXPLANATIONS OF THE DESCRIPTIVE PLATES. 
A GENERAL REFERENCE OF THE LETTERS EXPLAINING THE 
PARTS OF THE ANIMALS IN Puatss II. III. IV. V*. ann V**. 
A, Abdomen; the part of the body containing the intestines, and 
sometimes the nervous system and gills. 
A.— u. Abdominis umbones. Those parts of the abdomen which 
fill the umbones. 
An. Anus; the termination of the intestinal canal. 
Ap. Apertura; aperture applied to the opening of any cavity. 
"Ar. Apophysis: w. umbonica of the umbones; erd. of the hinge. 
Br. Branchie, gills: d. dextre, right ; s. sinistree, left; e. externz, 
external ; 7. internee, internal. 
Bss. Byssus, beard; composed of tendinous fibres, and is attached 
to the foot of some of the Class Ginglymaconcha or Bivalves. 
C. Cor, heart: a. auricule, auricles; v. ventriculus, ventricle or 
ventricles. 
Cl. Collum, neck. 
Cr. Cordiformis, heart-shaped. 
Crd. Cardo, hinge: d. dentes, teeth; c. cardinales or hinge teeth ; 
ca. the anterior; cp. the posterior tooth or teeth of the hinge. 
Dr. Dorsum, back. 
E. Epidermis, the skin or integument with the shell externally. 
H. Hepar, liver: h.r. hepatis regio, region of the liver. 
I. Intestma, mtestine: @. cesophagus; g. gegerium, gizzard; r. 
rectum ; v. ventriculus, stomach. 
Im. Impressio, impression, such as is made on the shell where the 
muscles are attached: c. cordiformis, cordiform, the umbilicus 
or navel. 
Im. cr. Cordiform impression. 
L. Ligamentum, ligament: a.a. ligamentum adductor anticum, 
anterior closing ligament ; a. p. ligamentum adductor posticum, 
hinder closing ligament; c. cardinale or hinge ligament; e. 
ligamentum externum cardinale, the external or cardinal liga- 
ment, which is placed over the teeth, and, when it resembles a 
hinge, is then termed gmglymoides; 7. ligamentum internum 
cardinale, the ternal ligament of the hinge. 
