MUSEUM OF COMPARATIVE ZOOLOGY. 413 



Genus LEPKTKLLA Vkrrill. 

 Lepetella tubicola Verrill. 



Plate XXV. Fig. 6. 



LepetcUa tubicola YqttxW, Am. Journ. Science, XX. p. 300, 1880; Proc. U. S. Nat. 



Mus., III. p. 375, Jan., 1881. 

 Lepetella tubicola Dull, I'roc. U. S. Nut. Mus., III. pp. 408, 411, April, 1882. 



Tlii.s ri'iuarkable species does not appear in the Blake collection, but, in addi- 

 tion to the northern localities referred to in the publications above cited, it has 

 been collected by the U. S. Fish Commission in the Gulf of Mexico, between 

 the delta of the Mississippi and Cedar Keys, Florida, at Station 2376, in 324 

 fms., mud, in worm tubes, bottom temperature 46°.5 F. I have figured the 

 dentition for comparison. A fossil specimen in the Jeffreys collection marked 

 Patella compressa Rayneval from Monte-Mario, and according to Tiberi (Jide 

 Jeffreys, P. Z. S. 1882, p. 674) also found living in the Bay of Naples, ap- 

 pears to be indistinguishable from Lepetella tubicola, so far as the shell is 

 concerned. 



Subclass ISO PLEURA. 



Some years ago,* in reviewing the article " Mollusca " of the new edition of 

 the Encyclopaedia Britannica, I pointed out that this Subclass is naturally 

 divided into two large groups; one the Polyplacophora^ including the Chitons, 

 which possess a developed and functional foot and exhibit a metameric repe- 

 tition of the primitive shell-sac; and the other the ChcEtodermida,\ worm-like, 

 with an abortive or rudimental foot, and (so far as known) without any evi- 

 dence of a shell or its equivalent. But as the term Polyplacophora has long 

 been in use for the Order including the Chitons, it is probably better to substi- 

 tute a new term for the Super-ordinal group. 



Super-Order POLYCONCH^. 



Order POLYPLACOPHORA. 



Suborder CHITONACEA. 



Super-Family EOCHITONIA. 



Head and tail plates similarly articulated. 



It was early recognized by Carpenter that the Chitons were separable into 

 two great groups, which he called the Regular and Irregular Chitons. To the 



* Science, pp. 730-732, June 13, 1884. 

 t Aplarophorn Fischer, Man. Conch., 1885. 



