28 



MOLLUSCA. 



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

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

 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. radicita 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. Mya truticata L. (Gaper). 



Fam. Gastrochaenidae (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. Oastroclioena clava L., Clavagclla 

 lacillaris Desh. Axperyillumjaraniini 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. Pliolas dactylus 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. 



Dicecious Mollusca without head, eyes, or heart, 



with tri-lobed foot, and 

 open at the two ends. 



tubular calcareous shell 



FIG. 505. Teredo 



navai : s, removed The Scaphopoda are allied to the Lamellibranchs. 

 fromitscaicareous The a d m i ra bl e investigations of Lacaze-Duthiers * 



tuoe, with elonga- 



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 Ceplicdophora. 



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 dudeveloppement du Den- 

 tale." Ann. des Sc. A'at., 1856-1858. 



