ON MOLLUSCA OF THE WEST COAST OF NORTH AMERICA. 357 



as rich in the minuter forms of life as are those that wash colder shores, or 

 even more so. Till the time of D'Orbigny, no one in the tropics seemed to 

 deign to bend his attention to what the amateur collector did not value ; but 

 Prof. Adams has already described many small species from Jamaica, and 

 80 from Panama, the latter simply by the examination of dead drift. In 

 these days of microscopic observation, most interesting results may be anti- 

 cipated if only dredgers will bring back labelled parcels of fine siftings from 

 deep waters ; and ordinary collectors, sieved sand or mud from the shores. 

 If shells were packed in the sieved sand of the place ; if they were always 

 sent home in the rough ; if those who decorticate their backs with acid, thus 

 destroying the minute microscopic sculpture which is often the best guide for 

 the discrimination of species, would only first brush them without acid, and 

 send the bottoms of the wash bowl to some microscopical malacologist, taking 

 care to wash only the shells from one spot at a time, and not to mix the dirt ; 

 we should soon acquire a knowledge of molluscan distribution which would 

 advance the science by rapid strides. Here do not apply many of the 

 sources of error common to larger shells. Ballast can scarcely mix its 

 anomalous transportations with the Cceca, Vitrinellce and Chemnitzice in the 

 interior of an oyster ; and the facts of distribution are as accurately seen in 

 these minuter forms as in the history of Cones and Olives. The remark 

 made by one of our very foremost naturalists, when it was first proposed to 

 investigate the Mazatlan shells, was that it was not likely that there should 

 be anything new among them ; as the large shells would be all the same as 

 Mr. Cuming's, and the small ones as those of Prof. Adams. And yet, com- 

 paring the 314 small species from Mazatlan with the 80 described from Pa- 

 nama, only 28 appear identical. The Ccecum Jirmatum, which is the abun~ 

 dant Panama form, is extremely rare at Mazatlan, where it is replaced by the 

 beautiful and still more abundant C. undatum, of which only one minute 

 specimen was perhaps found at Panama. Of the principal Panamic Vitrinella, 

 only one individual was found at Mazatlan ; where it is replaced by the shell 

 first termed V. clathrata, which turns out to be the same of which an aberrant 

 variety was imperfectly named and described from Panama as V. parva. 

 And so in other instances, as in the larger shells ; Chemnitzice being always 

 rare in individuals, fruitful in species, with many of a wide range ; Odostomice 

 not yet found at Panama ; Chrysallida communis, a coast shell, and very 

 abundant in both districts, while the other species from deeper water are 

 rare and local ; Bullidce and small Marginellce, diffused ; Rissoidce, local ; 

 and so on in ways on which it would be pleasant but not safe yet to gene- 

 ralize. As the same large Spondylus which furnished the Mazatlan minutiae 

 is also found in Panama Bay, where it is dived-for by the natives to burn 

 for lime, with all its Parapholades, Gastrochcence, Lithophagi and other rich 

 treasures, travellers in that region would do service to science by bringing 

 home a few valves, that it may be found how far the small nestlers correspond, 

 as the boring bivalves are known to do. 



But even with regard to the large shells, the distribution of many species 

 is anything but satisfactorily made- out. The fauna of the Central American 

 seas has never been properly published. A variety of new species are de- 

 scribed from Messrs. Cuming's and Hinds' collections, but of the old shells 

 found in the same stations we are left in ignorance. The practice of describing 

 only new species from voyages, instead of giving complete lists of those found, 

 very unnecessarily retards our geographical knowledge. The quotations 

 from Acapulco are like those from Dorsetshire or Guernsey in the old 

 British writers. What we yet know makes it far from improbable that while 

 one great type of shells extends at least from Guaymas to the Bay of Guaya- 



