284 GILBERT C. BOURNE. 



the large glandular cells on the edges of the laniinse. This 

 plate is firmly attached to the substratum on Avhich the 

 animal rests. There is no trace of calcification in it, and in 

 several of my specimens the bark of the root to which it was 

 fixed remains adherent, showing that there is no question of 

 the existence of an " ossicle/' which has been torn off when 

 the animal was detached. A comparison of this drawing 

 with Boutan's figures (loc. cit., pi. 14, figs. 18, 21, and 22) 

 leaves no doubt as to the identity, in all essential particulars, 

 of the byssus and byssus-gland of -Enigma with the 

 corresponding structures in Area tetragon a. The laminas 

 are much more numerous and the byssus cavity is relatively 

 wider and shallower in the former genus, that is all. 



Fig 18 is a very highly-magnified drawing of the outer end 

 of a single byssogenous lamina lying between two lamellfB o£ 

 the byssus of Enigma. The sides of the laminae are clothed 

 by a clear, generally-cubical, ciliated epithelium. I have no 

 doubt that this is a ciliated epithelium, and that it corrre- 

 sponds with the ciliated epithelium lining the byssus cavity 

 of other Lamellibranchia, as, for instance, in Cyprina 

 islandica (Carriere, 5), Dreissensia polymorpha 

 (Horst, 7), and Jousseaumia (Bourne, 3). Boutan, how- 

 ever, is of a very different opinion. He says, of similar cells 

 in Area, "Au-dessus de I'epithelium, en contact avec le 

 produit secrete, on aper9oit une striation tres nette qu'on 

 serait tente de prendre, au premier abord, pour des cils 

 vibratiles ; en realite, ce ne sent que des petits batonnets de 

 matiere secretee, absolument immobiles." Immobile they 

 may possibly be, as I suspect that their function is to afford 

 sufficient surface friction to prevent the byssus lamellae from 

 slipping out of place, but that they are true cilia is shown by 

 their insertion on a striated border of each epithelial cell, by 

 their correspondence with the cilia undoubtedly borne by 

 similar cells in other Lamellibranchia, and by the fact that 

 they are present where the secretory activity is in abeyance, 

 but absent where it is still in progress, which is the reverse 



