Dr. Lindstrom on Operculated Corals. 123 



only one valve, as in the kindred genera Calceola and BJiizopTiyllum, 

 it is composed of four valves, attached one to each side of the pyra- 

 mid. These four valves form two pairs, as the opposite valves 

 resemble each other. They meet with their apex in the centrum of 

 the coral, and overlapping each other in a sort of spiral way, to be 

 described further on, they completely close the calice of the coral. 

 In the specimen I first received, all four valves are left in their 

 place, and although two are sunk in the calice and somewhat 

 crushed, their outline may still be seen. In the other specimen, 

 only three valves are left behind. By this material, together with 

 valves found detached, a sufficiently accurate opinion of the shape of 

 this curious apparatus may be formed. Those valves that are at- 

 tached to the bottom side (that on which the coral rests when in its 

 natural position), and to the opposite or the uppermost side, have a 

 trapezoidal shape (See Fig. 6, PI. XIV., Geol. Mag., 1866). The 

 valves of the left and the right side are both triangular. The lateral 

 borders of all the valves are slightly curved, rarely straight. Along 

 the middle of their outside a groove runs from the nucleus to the 

 apex. It is broad and flat-bottomed in the trapezoidal valves, and 

 its section forms only an obtuse angle in the triangular ones. The 

 first and original part of the bottom valve, or what is called its 

 nucleus, is circular ; then it acquires a semicircular shape, and this is 

 again surrounded by other lines of growth giving the final trape- 

 zoidal outline. The nuclei of the other valves are from their first 

 origin already of the triangular or trapezoidal shape. Thus the 

 successive changes in the shape of the opercular valves are, I think, 

 clearly indicated. As the valves during their growth increase faster 

 at the apical than at their basal part, the nucleus comes more 

 closely to the basal line, and lies below the centrum (fig. 6, 

 pi. XXX. in Ofversigt Vet. Ak. Forhandl., 1865). Excepting the 

 lines of growth, no other sculpture is to be discerned. The dimen- 

 sions of the different valves are in the most complete specimen as 

 follows, viz : — 



Basal line. Length from Basal line to apex. 



Bottom valve 20 °*™- somewhat more than 10 °'™- 



Left-side valve 17 „ 10 „ 



Uppermost valve 16 „ 10 „ 



Eight- side valve 15 „ 9 „ 



Hence, the bottom valve is the largest, and the other valve 

 decrease in size as they are remote from that in a direction towards 

 left. The left-side valve covers with its right border the left border 

 of the bottom valve, and it is itself in the same way covered by the 

 left border of the uppermost valve, whilst the valve of the right side 

 reposes with both its borders on the adjoining borders of the upper- 

 most and the bottom valve. So that the last-mentioned valve is situated 

 beneath the three others with its borders, and its truncated apex is 

 hidden far below the apex of the opposite valve. I now suppose 

 that the situation and the size of the different valves signify their 

 different age and origin in such a way that the largest and deepest 

 situated is the oldest, and for a time the only valve existing that 



