THE SHELLS OF THE GULF OF CALIFORNIA. ' 205 



young C. nivea were some which under the microscope displayed a 

 much larger but smooth and imbedded nuclear portion. On comparing 

 these with similarly situated specimens from the west coast of Africa 

 and from other places, I found them exactly identical. They pro- 

 bably belong to the C. unguiformis of Lamarck. Now, it so happens 

 that Professor C. B. Adams, who in general described every shell of 

 Atlantic types as a new species, if found on the Pacific coast, in this 

 one instance felt constrained to adopt the Lamarckian name for the 

 unguiform slippers of Panama. It is not certain that in this one 

 instance he was correct. Some of the specimens he distributed under 

 that name are undoubtedly compressed and inverted forms of his own 

 C. nivea; for every species may take the form of unguiformis when 

 grown inside a dead spiral shell, especially with a hermit crab press- 

 ing against it. But there seems sufficient evidence to believe that 

 while each coast has its special species of slipper limpets, each one 

 of which assumes protean changes, there is this one species which 

 has been scattered, it may be in dead shells and on ballast, round the 

 world, and to be distinguished from all neighboring species by the 

 peculiar character of the nuclear whirls. It is too much the custom 

 among "collectors," and even among naturalists, to examine and 

 preserve only well-conditioned adult specimens. More may often be 

 learned from deformed and "ugly" shells; and especially from series 

 in all ages of development. 



We might easily fill the lecture with additional particulars concern- 

 ing the slipper-limpets, but it is time to pass on to other matters. 

 There is another family, the bonnet-limpets, (Capulidee,) nearly re- 

 lated to the cup-and-saucer tribe, but without the peculiar internal 

 appendage. Of these, two interesting species were found which 

 appear to be peculiar to the West tropical American fauna; while 

 others, the Hipponyx antiquatus, H. barbatus, and H. Grayanus, have 

 a very wide distribution in one or both hemispheres. 



Differing considerably in shape, but presenting remarkable points 

 of similarity in the habits of the animals, are the Vermetidae, (worm 

 shells,) of which some interesting forms belonging to new types were 

 found on our Thorn -Oysters. At first sight these shells would not be 

 distinguished from the serpulce, (shelly marine worms,) which are 

 found adhering to almost every dead shell from any sea-coast. The 

 shell-cases of both seem to crawl irregularly over the shell or stone 

 to which they adhere; and while some of the serpulaa assume the re- 

 gular spiral form of the Mollusks, some of the Vermetids assume a 

 looseness of growth as great as that of any worm. And yet the 

 animals which have exuded these similar habitations from their soft 

 skins, are more widely removed, the one from the other, than lions 

 are from snakes or fishes. The Serpulas belong to the same sub- 

 kingdom as the Insects and Crabs; and are, in fftct, red-blooded worms 

 with ring-jointed bodies, without head or eyes, and with the nervous 

 system pretty regularly diffused. While the Vermetids claim kindred 

 with screw-shells and Periwinkles, having their little heads, with 

 feelers and armed tongue-ribbons, and their nervous power collected 

 into irregular knotted centres. The true affinities with regard to 



