116 



PALjEONTOLOGY of NEW-TfORK, 



508. 1. DIPLOPHYLLUM CiESPITOSUM {n. sp.). 



Pl. XXXIII. Fig. I a-r. 



Corallum cylindrical or subturbinate in its young state ; stems coalescing at intervals and 

 increasing by lateral budding, csespitose or aggregated in large groups, which often grow from 

 a single base ; rays or lamellge numerous (about 50), thin ; centre of the cell with rays and 

 transverse septa ; external portion with fine rays and thin transverse dissepiments uniting the 

 lamellae, giving a kind of cellular structure to the outer portion of the coral. 



This species assumes a somewhat variable character, occuring in small groups, or rarely in 

 single stems with one or two buds on the sides ; but the more common form is that of numerous 

 individuals aggregated in large masses, the ends of the stems appearing on the surface of the 

 stone as in fig. 1 i. The manner of growth and aggregation is well shown in fig. 1 I, which 

 represents a small portion of a larger group exposed in the longitudinal direction, the whole 

 length of which is three times as great as the figure. Single individuals often grow for some time 

 independently, and then throw out numerous buds which become the base of a large group as 

 in fig. 1 m. Usually the specimens present only the radiating lamellae; these are stronger in 

 the outer portion of the cell, which is very distinctly separated from the inner portion as it 

 were by a cylindrical tube within the outer one. The interior is very frequently crystallized, 

 so that all structure is lost, while the external portion preserves the rays and the fine trans- 

 verse dissepiments uniting them. When weathered calcareous specimens are examined, the 

 cellular character of the external portion of the cup is distinctly visible ; but if the specimen 

 is much crystallized or silicified, then only the rays are visible. In good specimens, the rays in 

 the external portion of the cup appear denticulated on either side from the partial destruction 

 of the dissepiments. 



The interior structure varies to some degree, and the condition of preservation of the coral 

 has apparently an influence in this respect. 



In some instances the outer cellular portion is quite solid, and no rays or dissepiments can 

 be seen, and in such cases usually the centre presents only transverse septa. In others the 

 lamelte are all preserved, and the transverse septa are less conspicuous in the centre, and fre- 

 quently bent downwards or otherwise departing from their directly transverse character. In 

 many cases the lamellae are equally strong with the septa, and a lamellar structure only is 

 visible. In such examples the structure approaches that of Columnaria ; but there is no central 

 axis, and the cells are not in contact. This variable appearance, even in individuals of the same 

 group, proves that much care is necessary in the determination of the interior characters of a 

 coral in a fossil state, where one portion of the structure may be entirely absent, or appear 

 to play a very subordinate part, while in other instances some other part seems of undue 

 importance. 



The usual character observed in a longitudinal section is that of transverse septa in the iimer 

 portion of the cell, with the radiating lamellae rarely preserved. In the exterior portion, the 

 rays are always preserved with closely arranged transverse septa more rarely. But there are 



