130 BRITISH ITXK'ATA. 



others the tubercles are almost wholly confined to the 



e/ 



tubes, where they are always most numerous, and fre- 



V ti> 



quently compound. 



The mantle (PL XV, fig. 2) is delicate and is usually 

 tinged with yellow, sometimes with a rosy hue, and 

 is blotched with red on both sides ; the blotches, which 

 are rounded, become confluent on the tubes. The 

 freckling of opaque white is sometimes confined to the 

 track of the alimentary tube, and is accumulated in a 

 large spot in the ganglionic region ; in some specimens 

 nearly the whole mantle is suffused with red. 



The branchial sac (PI. XVIII, fig. 7) extends to the 

 bottom of the test, and has the minute plications well 

 defined ; the primary vessels are regularly disposed ; 

 the stomata are elliptical, shorter than usual, and fre- 

 quently do not extend the whole width of the space 

 between the primary vessels, and they are occasionally 

 irregularly disposed; the papillary membranes are 

 ample, with the thickened free margin narrow, and 

 scarcely if at all projecting beyond the longitudinal 

 bar. The longitudinal bars are delicate, with the sus- 

 pended membrane rather wide. The oral lamina (PI. 

 XIX, fig. 10) is broad, with the right side strongly 

 ribbed and the margin entire ; it terminates at the 

 bottom of the branchial sac immediately below the 



t/ 



mouth, where it is produced into an inconspicuous lobe 

 that appears to overhang the oral orifice. On the left 

 side of the mouth there are four or five, simple, 

 obscure, diagonal, ridges the left oral appendages. 

 The tentacular filaments are numerous, varying from 

 36 to nearly 50 ; they are variable in size, are long 

 and slender, and devoid of opaque white. The bran- 

 chial tubercle is a simple loop, open in front, and occa- 

 sionally with the extremities turned a little inwards. 



The ovary is a beautifully-branched, tubular organ, 

 ramifying over the left side of the intestinal loop : 

 the male organ is inconspicuous. The loop of the 

 alimentary tube forms a regular oval mass which lies 

 towards the dorsal region and extends from the bottom 



