1901.] 



MOTHEB-Or-PEARL OTSTEKS. 



381 



Species 5. Margarixieeba carchariarum, u. sp. (Texl-iig. 92.) 



Type B.M. 1901.2.28.48; Sharks Bay, pres. A. van 

 Noorden, Esq. 

 " Sharks Bay shell " of Mother-of-Pearl markets. 



Shell flat as in M. luargaritifcm, iu outline suggesting a small 

 example of M. maxima, but differing in the relatively greater size 

 of the rostrum and the more vertical posterior margin of the 

 nacre. Anterior teeth very abortive, in grown examples only 

 represented by a slight unevenness on the inner surface of the 

 hinge. Lateral teeth represented by a tiny lamina or elongated 



Text-fig. 92. 



Margaritifera caruharlaruni, uat. size. 



facet just posterior to the ligament. The posterior angle of the 

 nacre, where its margin meets the hinge-line, is a right angle. 

 There is no marked sinus in the hinder margin, but a slight notch. 

 The hinge is nearly as long as the autero-posterior measurement of 

 the nacre, the ratio of measurements being the following : — 



Hinge : length (aut.-post.) of nacre : depth (dors. -vent.) of 

 nacre : : 60 : 70 : 75, Average specimens measure about 8-10 cm. 

 in diameter. The hinge is relatively longer than in M. sugillata. 

 In the latter species the anterior margin of the nacre, ventral to 

 the byssal notch, projects considerably forwards. 



The lappet-like lip processes are crimped as in M. sugillata. 



