28 



MOLLUSCA. 



gaping, with thick epidermis. Two diverging cardinal teeth. Pallial indenta- 

 tion short, rounded. Siphons fused, with fringed openings. Mactra gtultorwm 

 L., Mediterranean. Lutraria Lain. 



Fam. Tellinidae. With two long, completely separated siphons ; edges of 

 mantle widely orien, bearing tentacles. Triangular foot. Tcllina bait tea Gin. 

 T. I'adiata L. Dona,e tntnculvs L. 



Fam. Myidae (Gapers). Mantle almost completely closed, with slit 

 for the protrusion of the short or cylindrically elongated foot, and very long 

 fleshy fused siphons. The valves gape at each end and possess 

 a weak hinge. Bury themselves deep in mud and sand. Sub-n 

 rag inn L., razor shell. Mi/a truiieata L. (Gaper). 



Fam. Gastrochaenidse (Tubicolidae). Shell thin, equivalve. 

 toothless, sometimes inserted in a calcareous tube formed by 

 an excretion of the mantle. Mantle with one small opening 

 anteriorly and prolonged behind into two fused siphons 

 with terminal openings. Gastrocltoena c7ai-a L., 4'lavaf/cUu 

 bacillaris Desh. Aspergillum javantMn Lam., Indian Ocean. 

 Fam. Pholadidae. Boring mussels. The valves of the two 

 sides gaping ; without cardinal teeth and ligament, but 

 with accessory calcareous pieces which lie either on the 

 hinge (Pholas) or on the siphons (Teredo, fig. 505). Mantle 

 with only small opening for the passage of the thick foot. 

 Siphons elongated. Bury themselves in mud and sand, or 

 bore into wood and even into solid stone, calcareous rocks 

 and corals. They form passages, from which they protrude 

 their fused siphons. Phulax dactyl us L. Piddock, Pit* 

 craxaata L. Ten-do nnvalh L. (Fig. 505) Shipworm, was 

 the cause of the famous dam- break in Holland at the 

 beginning of last century. 



SCAPHOPODA. 



Dioecious Mollusca without head, eyes, or heart, 

 with tri-lobed foot, and tubular calcareous shell 

 open at the two ends. 



FIG. 505. Teredo v 



navatis, removed The Scaphopoda are allied to the Lamellibraiichs. 

 from its calcareous Tne admirable investigations of Lacaze-Duthiers* 



tube, with elonga- 

 ted siphons (after first cleared up this group of Molluscs, which were 

 Quatrefages). f or a j Qn g t ' me k nowll as C irrobranchiata and 



grouped amongst the Gastropods. He showed that they are closely 

 related to the Acephala, and constitute forms transitional between the 

 latter and the Cephalophora. 



The shell is an elongated, somewhat bent, open, conical (with the 

 apex broken off) tube, and contains the animal, which has a similar 

 shape and is fastened by a muscle to the thinner lower edge of the shell 



* Lacaze-Duthiers. Histoire de 1 'organisation et du developpement du Den- 

 talc." Ann. des Sc. Nat.. 185(i-lS58. 



