29.^ ^{aOLOGICAL LITERATURE. 
united at tlieir entrance into the foot^ tliey assist also in the 
shutting of the valves^ and may he homologous to one of the 
two parts distinguished in the adductor of the Oyster and other 
Monomyaria v<^ithont foot. The byssus is a special secretion 
formed in two furrows within the anterior part of the foot. The 
ligament may he divided in Ti'idacnaj as well as in most other 
bivalves — into two portions, an outer or epidermal one, which 
shuts the two valves, and an inner one, fibrous, elastic, eflbr- 
vescent in acids, situated exactly between the valves, and having 
the function of opening the shell ; this latter portion frequently 
assumes an opalescent aspect (the lapis pavonius of elder au- 
thors), and is analogous to the inner ligament of MyUj Amphi- 
desmUy &c. In Pecten and Spondylus this portion is modified, 
not effervescent in muriatic acid ; and the outer portion is ab- 
sent in Spondylus ; in Pholas Candida the outer portion only is 
present. By some approximative experiments the force of the 
adductor muscle of a middle-sized IVidacna, 20-25 centimetres 
(about ten inches) long, was found to be equal to 4-7 kilo- 
grammes. 
The arrangement of the nervous, circulating, and digestive 
systems is fully described by the author ; there is no important 
difference from the general organization of* bivalves. The 
^^oculiform tentacles on the outer side of the edge of the 
mantle are more numerous near the branchial opening : they 
are placed beyond the edges of the shell when the animal is not 
disturbed ; and it would appear as if it really had a perception 
of light and shadow, the animal being more .infiuenced by dark- 
ness in its expansion than by a rather violent shaking of the 
vessel in which it is kept. All the individuals examined by 
the author (more than forty) proved to have ovaries, but no 
spermatogenous glands ; perhaps the latter may be developed at 
a certain season only. 
Order MYTILACEA, Guv. {Lucinacea^ Adams). 
LuCINIDiE. 
Lucina tenullamellUf sp. n., Brusina, Veiiiandl. zool.-bot. Gesellsch. Wien, 
1865, p. 37, Dalmatia, near L. sjnniferci. — L. undata, sp. n., Carpenter, Proc. 
Zool. Soc. 1805, p. 279, Gulf of California j L. tenuiscidpta, sp. n.. Carpenter, 
Proc. Ac. Nat. Sc. PhilaJ. 1865, p. 57, Puget Sound. 
Cryptodon sericatus, sp. n.. Carpenter, /. c. p. 57, Puget Sound. 
Ungulinid^e. 
Diplodonta savigmji, sp. n., Vaillant, Journ. Conch, xiii. p. 124, Suez. 
LASiElDiE. 
KelUa hoylici, spatangi, arid danili are described as new species by Brusina, 
Verb, zool.-bot. Ges. Wien, 1866, pp. 37 & 38, from Zara, Dahnartia. 
