Mr. W. Thompson on Xylophaga dorsalis. 159 



placed there without any preservative coating. It appears to 

 prefer black birch to any other timber, but does not like African 

 or American oak. The only successful preventive made use of 

 for preserving the dock-gates against the Teredo, Xylophaga, &c. 

 is Muntz's patent yellow metal sheathing, which is put on to the 

 height of thirteen feet ; it lasts for ten or twelve years. The 

 timber that is perforated is always covered by water. The depth 

 of water in the docks is from sixteen to eighteen feet. Red pine 

 is the favourite timber of the Crustaceans. 



On inspecting the pier, Major Martin could not observe that 

 the Xylophaga had committed any destruction, but saw that the 

 Teredo had been at work in some places. He cut off a piece of 

 the wood from the outside and sent it to me. It contained in 

 addition to the furrows of the Teredo, living specimens of both 

 Limnoria and Chelura. This pier has been about eight years 

 erected. I was also sent a portion of one of the dock-gates, con- 

 sisting of a piece of pine two inches in thickness, and within the 

 space of a few square inches containing the excavations of the 

 whole four species. It may give some idea of the frequency of 

 the Xylophaga' s perforations in the different pieces of wood, to 

 mention, that on an average at least one-half is occupied by its 

 burrows. The Xylophaga has never, like the Teredo, been ob- 

 served by my correspondent to form a testaceous tube or lining 

 to its cell. 



Xylophaga dorsalis, 



Turton seems to have been the first to notice, and under the 

 name of Teredo dorsalis it appears in his ' Conchological Dic- 

 tionary/ p. 185, and in his f British Bivalves/ p. 16 ; but in the 

 * Addenda/ p. 253, to the latter work, he constituted the genus 

 Xylophaga for its reception. His first specimens are noticed as 

 " from a piece of wood in Torbay." He subsequently obtained 

 " magnificent specimens of the Teredo navalis and this shell in 

 their most perfect state " from " fragments of a wreck known to 

 have been buried in the ocean for nearly half a century, near 

 Berry Head, at the entrance of Torbay." This author remarks, 

 that " like the Teredo, it inhabits the interior of the wood which 

 has been some time under salt water, penetrating to the depth of 

 from half an inch to an inch, forming for itself an oval receptacle 

 or cavity, and having a very small and single external orifice/' 

 p. 254. He observes, that " its habitation in wood naturally se- 

 parates it from the Pholas." But in this remark he forgot that 

 at p. 11 of the same work he had noticed Pholas striatus as 

 " taken from an old yard-arm on Brixham pier, and which had 

 been drifted in from the bay/' Very little would seem to be 

 known of the Xylophaga. Deshayes, in the second edition of 



