UNKNOWN ATLANTIC OR WEST INDIAN PORITRS. 99 



87. Porites West Indies x. 22. {P. Americana iiuxrtm sedis seeunda et vicesima.) 

 (PI. VI. fig. 2 ; PI. XVI. fig. 5.) 



[British Museum.] 



Description. — The corallum appears to ri.se as a small squat cluster or tuft. Its basal 

 stems are 2 cm. thick, diverge at wide angles from a common nodule of a dead former 

 growth, and curving upwards fork at about every 1 cm. apart. The t^irminals thus rapidly 

 produced, get smaller and smaller, and develop unequally ; some flatten ami commence to fork 

 at once, others remain aborted as stout mammilliform processes of varying lengths and about 

 8 mm. thick. These terminals also show the tendency to bend up into the vertical. The 

 living layer is from 4 to 5 cm. deep. 



The calicles are distinct, sliarply polygonal, but shallow, fairly uniform in size, 1*25 mm. 

 in diameter. The walls are low, but thin aud well-defined, the wall-thread l)eing con- 

 tinuous and straight, that is, with hardly any trace of the usual zigzag. The portions of the 

 septa springing from the top edges of the wall-tliread are usually quite short as small 

 echinulate knobs. The prolongation of the septa occurs lower down, where they stretch out 

 and join somewhat irregularly with one another, and with a columellar ring, which, seen from 

 above, appears as if it were continuous. From this ring the pali rise, and, for the most part, 

 surround a deep, open, central fossa, which is at times occupied by a small central tubercle. 

 Looking at the intra-calicular skeleton from above it appears to consist of an open network 

 built up of short, straight, smooth threads jointed together by finely echinulate knobs at the 

 nodes. It is very open, and the interseptal loculi are large, angular, and open. Some are as 

 large as the central fossa. 



The section shows a stout, close, axial, streaming reticulum, surrounded by a tliick ring of 

 much stouter skeleton, here fairly trabecular, there nearly solid. 



There is unfortunately only one specimen, from some unrecorded locality. The manner 

 of growth, and the type of the calicles leave no doubt whatever that it came from the West 

 Indies. It had been labelled Porites clavaria by Briiggemann. But the branching, with the 

 frequent abortion of the forking, and its stunted tuft-like growth differentiate it entirely from 

 Lamarck's type (see p. 81). It is unlike any other form in the collection. 



a. Zool. Dept. 1906. 1. 1. 8. 



88. Porites West Indies x. 23- (-P- Americana incertce sedis tertia et vicesima.) 

 (PI. VI. fig. 3 ; PI. XV. fig. 3.) 



[British Museum.] 



Description. — ^The corallum seems to have grown up slantingly to the horizon, perhaps 

 from the side of a rock ; the short basal piece is 2 cm. across and horizontally flattened. The 



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