22 
one on each side the upper part against the side of the body. 
Mantle with a small valvular hole, under the siphon. Foot with a 
byssal groove. Shell mequivalve. Umbo with a cartilage-slit. 
Cartilage internal, in a pit in each valve, with a peculiar shelly plate 
before it, or covering it. Periostraca often hispid. 
a. Siphons united. Valves subequal. Clavicle linear. 
1. LATERNULA. 
1. L. hispidula, t. 327, and fig. 6. 
Fig. 6.—Laternula hispidula. 
aa, adductor muscles. J, ligament. o, clavicle. g, gills. , palpi. 
b. Stphons separate at.the end. Valves unequal. Clavicle flat, 
covering the cartilage. 
2. LYonsia. 
1. L. coruseans, t. 327. f. 3. 
2. L. norvegica, t. 327. f. 1. 
3. MyvTILIMERA. 
1. M. patagonieca, t. 327. f. 2. 
c. Siphons separate. Valves unequal. Clavicle smali, subcylin- 
drical, 
4, THRACTIA, 
1. T. phaseolina, t. 327. f. 5. 
2. T. distorta, t. 327. f. 4. 
3. T. corbuloides, t. 327. f. 7. 
5. PERIPLOMA. : 
1... P. ovale, t. 327rain0,5t. das. 1. co: aa 
6. NEa@RA. 
1. N. costulata, t. 350. f. 2. 
2. N. cuspidata, t. 350. f. 3. 
7. Poromya. 
1. P. granulata, t. 346. f. 3. 
