39 
Suborder III. Mytilacea. 
Foot small, ligulate, byssiferous. Anterior adductor muscle 
small. 
Fam. 8. Mytilidce. 
Gills two on each side, dependent. Anus simple. 
a. Mytilina. Hinder part of the mantle only slightly produced. 
Anterior muscle small. Pedal opening large. Anal siphon 
short. 
1. Mytilus. 
1. M. edulis, t. 333. f. 4, 6, t. 366. f. 2. 
2. M. africanus, t. 366. f. 3. 
2. Modiola. 
1. M. tulipa, t. 369. f. 3, t. 373. f. 2. 
2. M. ?, t. 367. f. 1, 2. 
b. Crenellina. Hinder part of the mantle produced, forming false 
siphons. Pedal opening small. Anal siphon produced. 
3. Crenella. 
1. C. nigra, t. 369. f. 2. 
c. Lithodomina. Hinder part of the mantle more or less produced. 
Anterior muscles moderate-sized. 
4. Lithodomus. 
1. L. lithophagus, t. 366. f. 1, t. 373. f. 4, 4 a . 
2. L. patagonicus, t. 369. f. 4. 
Order V. Pectinacea, 
Mantle lobes free all round, without any separate opening for 
the out-going current and vent. 
Suborder I. Arcacea. 
Shell oblong or roundish. The anterior and posterior adductor 
muscles subequal. Mantle bearded behind. Vent, an attached? 
tube over the hinder adductor muscle, opening in a disk. Hinge- 
teeth elongate, nearly parallel to the hinge-margin, deeply grooved 
or divided into transverse interlocking plates. 
a. Foot lanceolate, subulate, angulated — for leaping. 
Fam. 1. Trigoniadce. 
Foot lanceolate, subulate, angulated, rather acute. Shell pearly 
within. Hinge-teeth two, divergent, deeply cross-grooved. 
1. Trigonia. 
1. T. pectinata, t. 358. f. 1, 1 a, 2, 5. 
