300 Bvlletin Vanderbilt Marine Museum, Vol. VII 



of Siphonaria characteristica Lovell Reeve, from the same locali- 

 ties, representing the more numerously and obscurely striated 

 variety with the interior dark brown, is deposited in the collections 

 of the British Museum of Natural History. 



Distribution: Galapagos Archipelago and Panama on the 

 west coast (Sowerby, Reeve) ; Peruvian Province, littoral (Dall) ; 

 Pearl Islands (Boone). 



Material examined: Seventeen specimens, collected at Can- 

 tadora Island, Pearl Islands, Panama Bay, Pacific Ocean, by the 

 "Alva," January 19, 1935. 



Technical description: This, the giant Siphonaria of the 

 littoral zone of the subtropical and tropical areas of the west coast 

 of the Americas, has considerable variation, even as exhibited in 

 the seventeen specimens of the present series. 



The shell is variously subcircular to long-ovate in marginal 

 contour, elevate, cone-like with apex obtuse, frequently eroded 

 in large specimens, subcentral to distinctly postcentral; the ex- 

 ternal surface radiately ribbed, these primary ribs frequently 

 very strong, ridge-like, with the interstices radiately striate, these 

 striae varying from vague to moderately strong, with an occa- 

 sional much coarser secondary rib which usually becomes obsolete 

 below the apex. Interior of shell variously opalescent smoky- 

 pearly gray to brown to purplish black-brown. Siphon impres- 

 sion very distinctly delineated in the interior as a narrow incom- 

 plete band with widened scars at each end, this band being de- 

 void of the pearly nacre (readily seen in plate 115). The ex- 

 terior of the shell is variously colored, the primary and secondary 

 ridges not infrequently being creamy white throughout their 

 length, or cream-white with occasional concentric brown, oliva- 

 ceous brown or brown-black markings; the marginal fourth of 

 the exterior is frequently deeper brown that the remainder, 

 which is usually lighter brown, the small apical area is frequently 

 white in the young and non-eroded specimens ; the central third 

 or more of the very large shells being white to gray-white, due 

 to erosion. 



