100 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 20 



The height to length ratio varies from small specimens to large ones, 

 the smaller being relatively higher, so that specimens of approximately 

 the same size must be compared. A few measurements will show this, 

 and also the differences in form. 



Length in mm 



without incrustation H/L ratio 



Peru 80.0 23.1 



Ecuador 63.2 25.3 



29.2 27.4 

 16.8 30.0 



Costa Rica 81.5 25.7 



61.0 26.3 



Lower California 59.0 32.7 



29.3 34.8 

 13.8 42.0 

 62.5 30.0 

 55.0 29.1 

 49.0 30.6 

 28.2 32.0 



The type locality for both Lithophaga attcniiata (Deshayes) and Litho- 

 domus inca Orbigny is Peru and apparently they both belong to the 

 slender form and are synonymous, especially as Orbigny (1846) gives 

 no records of attenuata Deshayes. The H/L ratio for L. inca is given 

 as 24. The differences in form between the typical southern elongate 

 specimens and the northern shorter ones are rather distinct ; but without 

 a larger amount of material it is not advisable to give the northern form 

 a subspecific name. 



The largest specimen, from Costa Rica, has a total length of 100 mm, 

 or 81.5 without the incrustation. 



Occurrence: Most of the collecting was done in shallow water, but sev- 

 eral samples were collected in deeper water down to 45 fms. All samples 

 are from within the known range of distribution. 



Distribution: Miller's Landing, Baja California, to Chile (Hertlein and 

 Strong) . 



Lithophaga (Labis) peruviana (Orbigny) 1846 

 Plate 10, fig. 58 



Lithodomus peruvianus Orbigny, Voyage dans I'Amerique Meridionale, 



vol. 5, Mollusques, 1846, p. 651. 

 Holotype: ? 



