THE LAMELLIBRANCHIA 27 
Vi 
the organs; the heart traversed by the rectum; two aortae. The shell 
with a pallial sinus ; the dorsal region protected by accessory calcareous 
pieces. Genera—Pholas, Linnaeus ; foot cylindrical ; siphons free near 
their extremities ; British. In Pholas there are four accessory plates ; in 
Zirphaea, Leach, two; in Barnea, Leach, one. Pholadidea, Goodall ; 
foot rudimentary ; siphons completely united and their extremity 
surrounded by a fringed disc ; shells elongated, in the adult prolonged 
posteriorly by a short calcareous tube, which surrounds the siphons ; 
British. Jowannetia, des Moulins; foot rudimentary ; 
siphons completely united ; shell globular, and the right ' 
valve prolonged posteriorly by a rostriform appendage. 
Aylophaga, Turton ; siphons separate at their extremities ; 
foot narrow ; shell globular with two accessory dorsal 
plates ; British. Martesia, Leach ; siphons long, united ; 
foot absent in the adult ; shell ovoid with a ventral plate 
in addition to the dorsal plates Faminy 2. TERE- 
DINIDAE, Fleming. Shell globular, covering a small 
portion only of the vermiform body. Heart on the 
ventral side of the rectum (Fig. 195, h); a single aorta ; 
siphons long, united to a large extent and furnished with 
two posterior calcareous “ pallets” (Fig. 247, II). Genera 
—Teredo, Linnaeus; a borer in wood; secretes an 
adventitious non-adherent tube; British. Xylotrya, 
Leach ; the pallets articulated. 
vi 
Sus-ORDER 9. ANATINACEA, 
Hermaphrodite Eulamellibranchia, in which the 
ovaries and testes are distinct and have separate orifices 5 
(Fig. 219, 0, t). The foot generally rather small. The 
mantle frequently presents a fourth orifice. The ex- Mi. 287. 
ternal gill-plate directed dorsally and devoid of a reflected, Teredo navalis, 
¥ ; » ventral 
lamella. Hinge of shell without teeth. aspect. I, shell; 
Famity 1. Turacipag, Dall. Mantle with a fourth 1), Lente se 
pallial orifice; the pedal orifice elongated; siphons branchial siphon ; 
; i siphonal mass 3. 
rather long, quite separate, and completely retractile vj, foot. 
and invertible. Shell with a deep pallial sinus. 
Genera—Thracia, de Blainville ; shell with a large spoon-shaped tooth ; 
British. Asthenothaerus, Carpenter ; shell without spoon-shaped teeth. 
Faminy 2. Pertpromrpak, Dall. Siphons separate, naked, completely 
retractile, but not invertible. Pallial sinus shallow; no ligament. 
Genera — Cochlodesma, Couthouy.  Pertploma, Schumacher.  Tyleria, 
Adams. Famity 3. ANATINIDAE, Gray. Siphons long, united, covered 
by a chitinous sheath, and not completely retractile. Foot slender. 
Pallial sinus well marked. Genera—Anatina, Lamarck. Shell thin and 
gaping, with spoon-shaped teeth. Plectomya, de Loriol ; fossil from the 
Jurassic and Cretaceous. Faminy 4, PHoLapomyipAE, Gray. Mantle 
extensively closed, with a fourth orifice. Siphons very long, completely 
united, naked, and incompletely retractile. Foot small, with a posterior 
appendage. Shell thin, with an external ligament and a well-marked 
