MOLLUSCA OP THE l CHALLENGER ' EXPEDITION. 89 



6. There actually are existing species whose distribution is 

 universal, no barriers having availed against their passage. 



7. Still there is no trace, even in these species, of essential, 

 lasting, and progressive change. 



I do not intend to overpress this point, for I allow that it pre- 

 sents merely negative evidence. I do not assert that there are 

 no species of Mollusca which have essentially, permanently, and 

 progressively changed. I only say there are some, even many, 

 which have not done so, that I do not know any which have, and 

 that the burden of proof lies with those who assert the positive. 

 Evolutionists are in the way of saying that a thing being 

 possible, is therefore probable, and consequently is true unless 

 the contrary be proved. I only wish to note that this is a 

 reversal of all the laws of evidence in any case of fact whatever, 

 and to add that, so far as I have had opportunity of observation, 

 no proof has reached me of progressive, permanent, and essential 

 change in molluscan development. 



In accomplishing so much as I have already overtaken, I have 

 been aided kindly, often, and in many ways, by Mr. E. A. Smith, 

 of the British Museum, who has, in the case of myself, as of 

 many others, helped with his great knowledge of the Museum 

 collection, and his large acquaintance with the literature of the 

 subject. I very gladly take this opportunity also of offering my 

 thanks to Dr. J. Gwyn Jeffreys, to Dr. H. Woodward, to Prof. 

 Seguenza, to Prof. Gr. O. Sars, to Prof. v. Martens, to the Mar- 

 quis de Monterosato, to Mr. William Dall, to Mr. Marrat, and to 

 many other friends. 



Siphodentalium, Sars. 

 8. S. honoluluense, n. sp. 



8. SlPHODENTALIUM HONOLULUENSE, n. Sp. 



July 1875. Beefs off Honolulu. 40 fms. 



Shell. — Cylindrical, bent and attenuated from about the middle 

 to the apex, toward the mouth very slightly contracted; of a 

 dull white translucency, and not glossy. Sculpture. The surface, 

 especially toward the apex, is faintly marked by microscopic, re- 

 mote, oblique, raised, encircling rings, parallel to which there are 

 fine scratches in the intervals. Edge of the mouth very oblique, 

 blunt. Apex not small, broken. Length 0*21 ; breadth, greatest 

 0*031, at mouth 0*028, at apex 0-016. 



LINN. JOUEN. — ZOOLOGY, VOL. XV. 7 



