CHAPTEK IV 



THE SCAPHOPODA 



CLASS III SCAPHOPODA, BROXN 



( = SOLENOCONCHA, de Lacaze-Duthiers). 



Definition. Marine bilaterally symmetrical Prorhipidoglosso- 

 morpha ; the body and shell elongated along the antero- posterior 

 axis and nearly cylindrical. The right and left margins of the 

 mantle are united ventrally and thus form a complete tube sur- 

 rounding the body, but with an anterior and a posterior aperture. 

 The head is somewhat rudimentary and devoid of eyes, but bears 

 two dorsal appendages furnished with numerous long filaments 

 (Fig. 183, I). The foot is cylindrical and adapted to digging. A 

 radula is present, but there is no ctenidium. The sexes are separate. 



Historical. These animals were formerly mistaken for tubicolous 

 Annelids, and afterwards were classed among the Gastropoda, near 

 Fissurella. Blainville, in 1819, was the first to rank them as a 

 distinct order of Gastropoda under the name " Cirrhobranchia." 

 In 1857 de Lacaze-Duthiers, as the result of a careful anatomical 

 investigation, created the division Solenoconcha to receive Dentalium, 

 making his new division equivalent to Lamellibranchia, and includ- 

 ing the two groups, together with the Brachiopoda, in a class 

 Acephala. Since de Lacaze-Duthiers' memoir, the Solenoconcha 

 have been universally recognised as a division equivalent to the 

 Lamellibranchia and Gastropoda, but the name Scaphopoda, proposed 

 by Bronn in 1862, has been more generally used for the sake of 

 uniformity. More recent investigations, however, have shown that 

 the Scaphopoda are more nearly akin to the Gastropoda than to 

 the Lamellibranchia. 



I. GENERAL DESCRIPTION AND EXTERNAL CHARACTERS. 



The shell (Figs. 181, D, E and 186) has the form of a very 

 elongated cone, slightly curved, the concavity of the curve being 

 dorsal : it is capable of containing the entire animal. The larger 



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