28 AXEL A. OLSSON 



under rocks at low tide, A large variety of turrids can generally be found 

 along Amador and Farfan Beach where they have been washed out of the 

 mud dredged from the ship channel and pumped onto the neighboring shore. 

 The Nassariidae is a large family with an indefinite number of species 

 (present estimate about 51); they include N. myristicata, N. luteostonna, 

 and N. pagoda, all common at Panama. Amongst the buccinids, there is the 

 curious Northia northiae which at night can often be seen plowing its solitary 

 way just below the surface with only the tip of its siphon showing. It has 

 related forms in the Caribbean Miocene, Phos or its allied genera are repre- 

 sented by several fine species; the largest is Cymatophos panamensis (clarki), 

 first described as fossil, later found in the Recent fauna. The Mitridae are 

 well represented and include some of the most sought for species (about 20); 

 they include the magnificent M. belcheri, often dredged off the Pearl Islands 

 and which has lately shown up in the Gulf of California; in Peru, M. swainsoni 

 is often cast up on the beach; it has a nearly smooth surface and a dark- 

 colored periostracum. The commonest of the shore Mitras are M. lens and 

 M. tristis, both found under rocks at low tide. Amongst the Muricidae (about 

 75 species in its widest meaning) are several showy species, often common at 

 favorable localities, Murex elensis, Muricanthus radix, and M. nigritus, 

 Hexaplex brassica and H. regius are often taken in large numbers by the 

 fishermen at Santa Elena, Ecuador, the conchs entangled in the nets set out 

 for crayfish (langosta). The Cypraeidae contain relatively few species and 

 most of these are small; the largest, C. cervinetta is perhaps best considered 

 as only a sub-species of the Caribbean C. zebra {exanthema). Characteristic 

 amongst CypraeaAWie shells are Trivia radians and Jenneria pustulata, both 

 found under rocks. Amongst the Cymatiidae are two species of Distorsio 

 (decussatus and constrictus) with similar forms in the Caribbean, the large 

 Cymatium tigrinum, formerly common in Panama, and several Bursa. With 

 the exception of the Scotch bonnet, the Semicassis centiquadrata, the other 

 members of the family Cassididae are relatively uncommon. Special mention 

 should be made of Malea ringens, one of the most characteristic of present- 

 day Panamic gastropoda, but represented in the Caribbean Miocene by 

 hardly distinguishable forms. This species extends south to the Lobos Islands 

 in Peruvian waters where it grows to a large size. Along the Ecuadorian 

 coast, M. ringens is relatively rare, replaced by the smaller, heavier shelled 

 M. crassilabris Val., which the author regards as a good species. 



Pelecypoda 



The pelecypods are probably the best known of Panamic-Pacific 

 mollusks, and in addition to this study, the class has been revised by Hert- 

 lein and Strong in a series of excellent papers published in Zoologica be- 

 tween 1940 and 1950. Two other important papers have also appeared, one 



