28 MOLLUSCA. 



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

 tion short, rounded. Siphons f used, with fringed openings. Mactra stultoru m 

 L., Mediterranean. Lutraria Lam. 



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

 mantle widely open, bearing tentacles. Triangular foot. Tellina baltica Gm. 

 T. radiata L. Donax trunculus 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. Solen 

 vagina L., razor shell. My a t nine at a L. (Gaper). 



Fam. Gastrochaenidae (TuMcolidae). 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. Gastroclicena clava L., Clavagclla 

 lacillaris Desh. Aspergillum javanum 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 (Pliolas) 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. Pliolas daciylus L. Piddock, Ph. 

 crassata L. Teredo navalis 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 Jieart, 

 with tri-lobed foot, and tubular calcareous shell 

 open at the two ends. 



Yia. 505. Teredo 



removed The Scaphopoda are allied to the Lamellibranchs. 

 The admirable investigations of Lacaze-Duthiers * 

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

 for a long time known as Cirrobranchiata and 

 grouped amongst the Gastropods. He showed that they are closely 

 related to the Acephala, and constitute forms transitional between the 

 latter and the C ephalophora. 



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- 

 tale." Ann. des Sc. Nat., 1 850-1858. 



