162 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. 37. 



XYLOTRYA DRYAS, new species. 

 Plate 25, figs. 2, 3, 5, 6, 7. 

 From the stem of a living mangrove at Estero del Palo Santo, Tumbes, Peru. 



As a rule, animals belonging to this family excavate their burrows 

 in dead wood, not living trees, though the African mangrove of Sene- 

 gal is bored in the living state by a true Teredo, which received the 

 name of T. senegalensis from Blainville. The present species so far 

 as noted is the first to be reported from living trees in America, and 

 the first of the genus Xylotrya known to have this habit. 



The external surface of the valves, beginning in front, is dividetl 

 into five areas, of which the first might perhaps be regarded as internal 

 rather than external, though when the muscles are removed it faces 

 outward. It is in reality a myophoric surface, free from periostracum 

 and in life supports very powerful muscles, which hold the two valves 

 together; the surface of this area is rather irregular, the dorsal ex- 

 tremes of the area in the two valves project in blunt points; this area 

 is separated from what is generally called the anterior area of the 

 valves by a deep sulcus, the posterior slope of which terminates in a 

 rounded bounding ridge; the anterior area proper is concentrically 

 sculptured by regular, low, sharp, equally spaced, fine lamellae with 

 slightly wider interspaces; these are crossed by extremely sharp, fine, 

 close, microscopic, radial striaj; the vertical width of this area is a 

 little more than the witlth of the premedian area; the sculpture 

 changes abruptly at the junction of the two areas and the angle at 

 the junction of their ventral margins, as of the sculpture, is about 97°. 

 The premedian area is similarly sculptured, but the lamellse are rather 

 smaller and more close set than in the anterior area, while the radial 

 striae are coarser and deeper, showing distinctly on the tops of the 

 lamellae. The postmedian area is feebly concentrically striated, cov- 

 ered with a thin glossy periostracum and more or less brown stained 

 by the mangrove sap; it is separated from the posterior lobe by an 

 angle; the posterior lobe or area is similar in surface and forms some- 

 what less than a semicircle, low and evenly rounded. The two valves 

 are held together by strong muscles, chiefly attached to three myo- 

 phoric areas. The first of these, anterior and looking outward and 

 forward, has been described ; the second forms an irregular concavely 

 excavated rough surface extending from the anterior sulcus to the 

 angle between the postmedian and posterior lobes of the shell. This 

 surface includes much of the dorsal edges of the original valves, and 

 when the muscles are removed the appearance is as if the valves have 

 been badly eroded, but the condition is the same in the youngest 

 valves I have been able to examine, and if, as seems evident, a con- 

 siderable portion of the umbonal surface is missing, it has unques- 

 tionably been removed by absorption, and not by external erosion. 

 The styloid processes are broad and long, extending nearly to the 



