27G THE VOYAGE OF H.M.S. CHALLENGER. 



The interior is white aud not glossy, but this may not always be the case in specimens 

 found living, the only shells under examination having been dredged without the animals. 



Length 43 mm., height 22, diameter 13|^. 



Habitat. — Station 207, west of the Island of Luzon, Philippines, at a depth of 700 

 fathoms ; also Station 191, near the Arrou Islands, in 800 fathoms. 



The specimens from the latter locality have not attained so large a size as the single 

 example from off the Philipjjines, the dimensions of which are given above. They are 

 not quite so gently arcuate at the posterior end, have the ventral outline sHghtly convex, 

 and exhibit a few distinct scratch-like striae across the anterior lower portion of the 

 valves at right angles to the lines of increment. In the type I also find a few traces of 

 similar striae. 



This species belongs to that section of the genus which includes Modiola arhorescens, 

 Chemnitz, Modiola glaherrima, Dunker, Modiola degans, Gray, Modiola perfragilis, 

 Dunker, and a few others, characterised by light fragile shells with a highly glossy 

 surface. The last of the above-mentioned forms most resembles that now described. It 

 is, however, much narrower, has no dorsal plications or wrinkles, and is not quite so 

 fragile and iridescent within. 



Both the large and small specimens of Modiola watsoni, so named in honour of my 

 friend the Eev. R. Boog Watson, have more or less of a rust-like incrustation adhering to 

 the anterior or umbonal region, which in the former has stained the surface yellowish -brown. 



Lithodomtis, Cuvier. 



Lithodomus antillarum (Philippi). 



Modiola (Litlwphagus) antillarum, Philipiji, Zeitschr. Malakozool, 1847, p. 116. 



Modiola antillarum, Philippi, Abbild., vol. iii. p. 20, pi. ii. fig. 4. 



Lithodomus antillarum. Reeve, Conch. Icon., vol. x. pi. ii. fig. 7. 



Lithodomus niger, d'Orbigny, in Sagra's Hist. Cuba, Molliisques, vol. ii. p. 331, pi. xxviii. 



figs. 10, 11. 

 Lithophaga nigra, Dunker, Conch.-Cab., eJ. 2, p. 12. 



Habitat. — Bermuda, boring in coral. 



The Lithodomus antillarum described by d'Orbigny in the above work (p. 332) 

 appears to be identical with Lithodomus corrugatus of Philippi. 



Lithodomus appendiculatvs (Philippi). 



Modiola a.ppendiadida, I'hilippi, Abbild, vol. ii. p. 150, pi. i. fig. 4. 

 Lithodomus ai:>pemlicidatus, Reeve, Conch. Icon., vol. x. pi. iv. fig. 21. 

 Lithophaga appendiadata, Dunker, Conch.-Cab., eJ. 2, p. 15, pi. v. fig. 14. 

 Lithodomus hisulcatus, d'Orbigny, in Sagra's Hist. Cuba, MoUusques, vol. ii. p. 333, pi. xxviii 

 figs. 14-16. 



Habitat. — Bermuda, boring in lioral {Ocidina hermudiana). 



