222 SYNOPTIC COLLECTION. 



out umbilicus is represented in the Collection by a number 

 of specimens which may belong, as we have already 

 pointed out, to as many different series. 



lanthina has a spiral shell resembling Lunatia in shape. 

 It is translucent with violet colored areas. This mollusc 

 makes a swimming float of cartilaginous air sacs which 

 serves to keep it at the surface. To the under surface 

 of this float are attached the egg capsules (see No. 456). 



The egg cases (No. 457 ; see erect part of Section) of 

 Bucdnum undatum Linn., are in masses. The shell is 

 closely coiled and ribbed at right angles to the lines of 

 growth (see No. 458). 



Turbo setosus Gmel. (No. 459) begins as a smooth, col- 

 orless or yellow shell, then becomes ridged and is of a 

 vivid green color, while the older whorls are dark green, 

 marked by reddish brown spots. The aperture is entire. 

 Litorina littorea Linn., has been imported from Europe, 

 and in 1872 appeared in Massachusetts; since then it has 

 spread with remarkable rapidity. The British form (No. 

 460, L. obtusata Linn.), is a smooth spiral without an um- 

 bilicus. The shape varies like that of most littoral species, 

 some specimens having a spire of three or four whorls, 

 while in others the spire is depressed so that all the whorls 

 excepting the last or body whorl are on a horizontal plane. 

 Our New England species generally has a sharp spire and 

 revolving lines on the whorls, while the color is a dingy 

 brown or red. The external horny layer when fresh is a 

 chestnut brown. 



Cydostoma elegans Drap. (No. 461 model), is similar to 

 Litorina in many structural points but it has become more 

 specialized by losing gills and breathing air by means of 

 lungs. In a classification based strictly upon the struc- 

 ture of the breathing organs the Cyclostoma would be 

 placed with the Pulmonifera, but it is not probable that 

 this would indicate its relationships. The model repre- 

 sents the animal with the foot expanded ; at the anterior 

 end is the head with two tentacles extended, at the base 

 of which are the eyes. 



