1897.] NATURAL SCIENCES OF PHILADELPHIA. 299 



EXTERNAL FEATURES OF YOUNG CRYPTOCHITON. 

 BY HAROLD HEATH. 



The genus Oryptochiton includes the most highly modified indi- 

 viduals in the order of the Polyplaeophora so far at least as exces- 

 sive growth of the mantle and the consequent diminution in size of 

 the tegmentum is concerned. In the adult no trace of the tegmen- 

 tum is visible, the articulamentum alone remaining, being com- 

 pletely hidden within the mantle. While it is held by many that this 

 represents the last stage of a process by which the mantle gradually 

 encroached upon and finally destroyed the tegmentum, Reincke 1 

 considers it to be a primitive condition from which the remainder of 

 the Ohitons have been modified. The following observations on the 

 young of Cryptoehiton stelleri, are of interest in this connection. 



In many places along the coast of California this species is of fre- 

 quent occurrence. In and about Monterey Bay they are quite com- 

 mon out beyond tide marks, where the water is from six to twelve 

 feet in depth. Sometimes they may be seen in the dark hollows and 

 crevices, slowly moving about in search of food, which consists mainly 

 if not entirely, of plants. 



On July 14, 1896, two young specimens were found on the under- 

 side of stones at the extreme low tide mark. They were placed in 

 an aquarium at the Hopkins Seaside Laboratory and were kept for 

 several weeks but they were always sluggish, remaining quiet for 

 days together in the dark corners or under stones. They did not 

 exhibit any peculiarities worthy of note. 



They were oval in outline, the broader end being anterior, and 

 were of the same size, having a length of 27 mm. and greatest width 

 of 15 mm. 



Adult Cryptoehiton are of a dark red color, sometimes obscurely 

 blotched with white. The young were unlike in coloration, one hav- 

 ing a light orange-yellow color shading to orange on the mid-dorsal 

 line; the other was of a light green also darker in the region of the 

 shell. In both the tint was lighter on the ventral surface. The 

 bunches of calcareous spines that cover the dorsal surface contain 



1 Zeit. fiir wiss. Zool. Bd. XVIII, 1868. 



