82 



Tlic first biistle-tuft occurs immediately behind the collar 

 and is unaccompanied by hooks. The bristles of the anterior 

 region form vertical rows, the upper eight or ten bristles have 

 tapered tips with wings (Plate VII., hg. 38). They are followed 

 by two rows with spathulate tips (Plate YII., fig. 39) the upper 

 row having longer tips often with a central filament, and in 

 some indications of transverse rows of spikes, the lower having 

 broader tips (fig. 40). 



The anterior hooks (Plate VIL, fig. 41) have a prominent 

 fang and a crest or crown with fine serrations. The anterior 

 curve is bold, and the posterior process long. 



Posteriorly the tips of all the bristles are produced as long 

 processes, the wings being rather abruptly widened above the 

 slightlv constricted end of the shaft (Plate VII., fig. 42). The 

 posterior hooks are smaller, have a rounded anterior curve and 

 a shorter posterior process. 



The tubes inhabited by this form are often grouped together 

 in longitudinal bundles, and are composed of tough hardened 

 secretion coated with sand. They resemble those of the 

 British ''Sabclhi siixicaiui," though they are larger. In the 

 same way the tips of the horny tubes are sometimes closed by 

 being bent. In the larger tubes the grains of sand are coarser, 

 and fragments of shells are added. In all cases the horny 

 secretion is characteristically firm and niore or less brittle. In 

 one the tubes projected from a whitish mass of a compound 

 ascidian, the sandy tube being in the centre and forming the 

 axis on which the ascidian was supported. De St. Joseph finds 

 that the tubes occur in a similar way between Cyiithici gloiiicnifd 

 and the granite rocks. In the Channel Islands as well as on 

 the southern coast of England this species is very common. 

 In the former it is abundant in oysters, Pcctcii, Aiioiiiid and 

 other dead and living shells, in Balani covering the sides of the 

 Gouliot caves at Sark, the tube is coiled beneath the Balani and 

 pierces the latter to reach the surface. The species likewise 

 perforates CcUcpora, and even bores quite through the valve of 

 a living Pi'cfcii />//.->/o. It often occurs in the same oyster shell 

 with Giisirocluvita, Polvdora and Clioiic, and it sometimes- 

 places its tubes in groups in convenient fissures of the shell 

 without boring, so that they can be dislodged cii masse, as has 

 been the case in a series from South Africa. Another site is 

 under emptv limpet-shells amongst muddy debris, part of each 

 tube being inserted into a perforation in the shell ; while again 

 the cracks and fissures of the rocks near low-water mark afford 

 a verv favourite habitat, and the tubes often project through 

 incrusting sponges and ascidians both simple and compound. 

 As a rule the tcnigh hornv tube has grains of sand protecting 

 the exposed portion, whilst the part immersed is hyaline and 

 more delicate. The tunnels in shell, limestone and chalk are 



