MONOGRAPH OF AMERICAN SHIPWORMS. 25 



tached there is left a bony, acorn-shaped nucleus. Diameter about 

 3 millimeters. 



" From timbers of ships that have cruised in the Pacific. 



" This species is remarkable for its minute size and globular form, 

 its large sculptured claw area, and its peculiar pallets, to which 

 there is nothing similar among the species of true Teredo^ and which 

 have no cups or transverse segments as in Xylotrya. The burrows 

 do not run in the course of the grain of the plank, but transversely, 

 and stand thickly side by side so as to resemble honeycomb, or the 

 organ coral, Tubiyora musica; the tubes are lined b,y a thin gummy 

 or horny coat,-and terminate in a concave calcareous disk with a sort 

 of transverse scar on its outer or convex face. I have not been able 

 to detect any transverse partitions. If on these accounts it should be 

 considered as entitled to generic distinction, it may be denominated 

 Lyrodus.'''' 



TEREDO (LYRODUS) BIPARTITA Jeffreys. 

 TWO-PAKTED SHIPWORM. 



Plate 21, fig. 1 ; plate 33, fig. 4. 



1860. Teredo bipartita Jeffreys, Ann. Mag. Nat. Hist., ser. 3, vol. 6, p. 123. 

 Shell subglobular, the anterior part having a sinus at the extreme 

 anterior edge, which is covered by a callus that is slightly reflected 

 outwardly over the shell. The rest of the anterior portion is covered 

 by a series of dental ridges which expand fan shaped from the an- 

 terior portion backward. At the posterior margin the spaces that 

 separate them are about as wide as the ridges. These ridges are 

 marked by exceedingly fine clenticulations at their free border. 

 There are 53 of them in the specimen figured. The posterior edge of 

 the anterior portion is joined to the anterior portion of the median 

 part in a straight line that extends from the ventral edge to the 

 umbones. The posterior median portion is marked by slender ridges 

 Avhich join the dental ridges of the anterior part at almost right 

 angles. These ridges are separated by narrow grooves, and are 

 strongly denticulated on their free margin. The middle median por- 

 tion is marked by a depressed groove, across which the upturned 

 enfeebled and subobsolete terminal portions of the dental ribs extend. 

 The posterior portion of the median part is a little wider than the 

 anterior, and is marked by strong oblique lines of growth. The 

 posterior part forms a slender, small auricle, which is marked by 

 feeble incremental lines. The interior of the shell shows that the 

 auricle projects slightly over the posterior median part. The pos- 

 terior median part shows a strong median groove that extends from 

 the umbones to the ventral portion of the shell. The latter part is 

 armed with a strong knob. The blade is very slender, sickle shaped, 

 extending three-fourths of the way across the inside of the shell. 



