THELEPUS. 169 



which perforated stones, though Linnaeus subsequently placed it Under the Terebellids. 

 Its habit of occurring in fissures of rocks with its siphonal tunnel had misled Kahler. 



Dalyell's (1853) small examples constructed cylindrical sheaths of sandy or muddy 

 particles and insufficient to cover the body. The sheath was frequently abandoned. 

 They also, he narrates, produce a "real cobweb" of mucous threads with which they 

 cover themselves and support the spawn. 



The laxity of De Quatrefages' arrangement (1865) and the subsequent confusion 

 is illustrated in this species, which was included under the genus Idalia, and afterwards 

 described as a new form under the title Heterophil selia Bosci. 



Malmgren's account (1865) was probably drawn from specimens in the British 

 Museum, and his description refers to Leprea lapidaria, which had been confounded with 

 Dalyell's L. textrix in the collection. 



Marenzeller (1884) gave a careful digest of the literature of this species, and 

 corrected the synonymy up to date. 



Gravier 1 (1906) thinks that this species perhaps secretes an acid, which enables it to 

 attack the calcareous masses amongst which it lives. It is nowhere more abundant than 

 in the gneiss of Guernsey in fissures and crevices of the rocks, where the secretion of an 

 acid would not be effective, so that the secretion is not always of service in this 

 respect. 



De St. Joseph 2 (1906) found a Rotifer, Discopus synaptse, on the skin of this form 

 at St. Jean-de-Luz. 



In the British Museum, preparation 66 . 8 . 20 . 14, attached to the shell of a Pinna 

 from Polperro, and labelled Terehella constrictor, is Leprea textrix. 



Genus CLII. — Thelepus, Leuckart, 1849. 



Lumara, Stimpson, 1855 ; Neottis, Malmgren, 1865 ; Phenacia, Heterophyselia and 

 Heterophenacia, De Quatrefages, 1865; Thelepodopsis, Sars, 1871; Venusia, Johnston, 

 1855; Heteroterebella, Panceri. 



Cephalic lobe with a well-marked dorsal collar, the external rim passing to the 

 ventral surface, and joining the lower edge of the supra-oral arch, the intervening space 

 being occupied by the inner tongue-shaped process and the fillet of the post-oral segment. 

 Anterior surface of cephalic plate occupied by the tentacles. Numerous ocular specks. 

 Body typical, though the ventral scutes are often indistinct. The dorsal surface 

 frequently has rounded glandular furrows. Branchiae a filiform transverse series (two or 

 three on each side, rarely one) on the second and third segments. Setigerous processes 

 commence on the third segment, and extend to the posterior end. The avicular hooks 

 begin on the fifth segment and also continue to the penultimate segment in a single row, 

 and in some the row ends in a loop or circle. JNephridia increase in size from front to rear. 



Tube long and membranous, with fragments of shells, zoophytes, and other foreign 

 structures externally. 



Grube (1878) adopts the title Phenacia of De Quatrefages for this group. 



1 ' Nouv. Archiv. Mus. Paris/ 4 e ser., t. viii, p. 210. 



2 ' Ann. Sc. nat./ 9 e ser., t. iii, p. 175. 



191 



