120 K. MITSUKURI : STUDIES ON 



between those mentioned above. They may all be mixed 

 together in one individual ; but there is a tendency for some 

 one type to bo predominant in one individual. Buttons and 

 tables are more or less scattered in the interspace between the 

 groups. 



Tables have generally a spiny margin. In some, only the 

 four central holes with the spiny margin are present in the 

 disk (b). Very frequently a more or less complete second circle of 

 holes is present : this is probably the commonest form (a). In one 

 specimen (No. 1227) tables are plump, and may have a third 

 circle of small holes in addition. Disks with smooth margin are 

 occasionally seen (c). The spire may be rudimentary, but oftenest 

 has one cross-beam and ends in a crown which has 7 — 12 teeth. 

 The small Tosa specimen (No. 1194), measuring 2.7x1.2 cm., has 

 very peculiar calcareous deposits and is referred to this species 

 with considerable doubt. In it tables with spinous margin are 

 rare ; by far the largest number of them have smooth crenate 

 margins and a second circle of holes, their sizes varying consider- 

 ably. Occasionally among them, large tables (0.12 mm.) a:e found, 

 with four very large central holes and some smaller ones added. 

 These large tables seem to have a tall spire, probably with two 

 cross-beams. Buttons in the specimen are half-sided. In other 

 characters, it apiJroaches the other specimens of //. pardalis. 

 Considering its small size, it is probable that we have here to do 

 with a young individual of the species. As ah'eady mentioned, 

 tables with smooth margin are found in other individuals too, but 

 not proportionally so numerously in relation to spiny- margined 

 ones as in the small specimen under question. Since, now, the 

 spiny margin is simply an expression of an incomplete formation 

 or of the degeneration of the table-disks, it seems possible that 



