452 BULLETIN" 103, UNITED STATES NATIONAL MUSEUM. 



had been found in Oolitic rocks, it would have passed for a small 

 variety of Isastraea tenuistriata." 



I examined the type of this species in the Geological Society of 

 London collection (No. 12,929), and it is represented by plate 120, 

 figure 1. It belongs to the genus Siderastrea. There are more 

 than four cycles of septa. The septal trabeculae are narrow, and 

 produce fine dentations on the septal margins. The estimated number 

 of teeth on the margins of the longer septa is about 20; the synap- 

 ticulae are fine and are crowded in two or three rings near the wall, 

 which is narrow and continuous. The columella is weakly developed 

 and evidently had a finely papillary upper surface. 



I collected in Antigua, station 6888, one-half mile north of McKin- 

 non's mill, in the Antigua formation, one satisfactory specimen of 

 this species. It is of massive, subcolumnar growth form, is about 

 105 mm. tall, and is 82 by 92 mm. in diameter near the top. The 

 basal part is appreciably narrower than near the summit. The 

 calices are shallow; corallite walls thin. Acalice 4.5 by 8.25 in diam- 

 eter has about 80 septa. Septa composed of small trabeculae and 

 correspondingly have finely dentate margins. Synapticulae delicate 

 and crowded. 



This species is very abundant in the Oligocene deposits of the West- 

 Indies and the Canal Zone. Description of or notes on specimens 

 from the different localities follow. The next specimen to be de- 

 scribed is essentially typical, and as it is in a better state of preserva- 

 tion than the one from Antigua, it is more satisfactory for purposes 

 of illustration. 



Description of a specimen from near Lares, Porto Rico (pi. 120, 

 fig. 2, 2a). — Corallum massive, rounded above, basal portion some- 

 what expanded. Greater diameter of base, 106 mm.; lesser diameter 

 of base, about 65 mm.; height, 65 mm. 



Calices polygonal, rather large, diameter (measured from summit 

 to summit of wall) from 4.7 to 7.4 mm., 5 to 6 mm. the usual 

 diameter. Near the edges the calices are shallow, higher up on the 

 corallum they are excavated and moderately deep. The outer ends 

 of the septa are arched on the upper part of the corallum, may be 

 somewhat flattened near the wall; lower down they may be depressed 

 across a wide area, with a very shallow calicular cavity; in a few 

 instances a depression corresponds in position to the upper edge of 

 the wall. Wall usually distinct, narrow, zigzag. 



Septa very crowded, thin and numerous, 70 in a calice 4.6 by 7.4 

 mm. in diameter, 76 in one 5.75 03^ 7.6 mm., 74 in one 5.5 by 6.3 mm. 

 in diameter. They are so crowded that it is difficult to make out 

 the cycles. The primaries appear to be free, the other septa form 

 groups around the secondaries. Septal margins finely beaded; 

 about 26 dentations on a large septum, an actual count for an entire 



