ARNOLD— THE PALEONTOLOGY AND STllATIGRAPHY OF SAN PEDRO. 



89 



There are four complete cycles of septa, and many members of the fifth, but the fifth is not 

 complete. The septal margins project very slightly above the upper margin of the corallum wall; 

 the margins of the members of the first and second cycles, and those of the third cycle when members 

 of the fifth are present, are slighdy more prominent than the margins of the members of the higher 

 cycles. The septal faces are densely granulated, and the granulations show a decided tendency 

 toward elongation along the courses of the septal trabecular. The septa are crowded, those of the 

 first, second, and third cycles are thick and strong; when members of the fifth cycle are present those 

 of the fourth are quite thick, but are thinner than the older septa. 



The pali are well developed, and are shown in great perfection on the type specimen. 

 They are broad and simple, and not bilobed. Those before the septa of the first cycle are the nar- 

 rowest; those before the septa of the second cycle are slightly wider, and those before the septa of 

 the third cycle are still wider. The inner margins of the pali before the septa of the first, second, and 

 third cycles form a crown bordering the outer edge of the columella. In those half or quarter sys- 

 tems in which septa of the fifth cycle are present, pali stand before the members of the fourth cycle. 

 These pali are large, but stand back from the columella. In such cases the pali join the members of 

 the fourth cycle to the sides of the included members of the third. When no pali are present the 

 members of the fourth fuse by their inner margins directly to the side of the included member 

 of the third. When members of the fifth cycle are present, they curve toward the included 

 member of the fourth. There are no pali before the youngest septa in any given system. Margins 

 of the pali entire. 



The calice is shallow, widely open Its ends, corresponding to the ends of the longer trans- 

 verse axis, are very slightly depressed. The upper surface of the columella is flat; it consists of the 

 rounded upper terminations of a large number of papillae. The pali, excepting those of the fourth 

 cycle, form a crown around the columella, as has already been stated. 



Dimensions. — Greater diameter of calice, I2 mm.; lesser diameter of calice, lo mm.; height 

 of corallum, i8-J- mm. 



Locality. — 8an Pedro, California. 



Geologic Horizon. — Pleistocene. 



I'ype. — From the collection of Ralph Arnold. 



If the description first given is compared with the table showing the chief 

 diagnostic fcatnres of Verrill's species, it will be evident that the only species with 

 which comparison needs to be made is P. atearnsi. At the same time, certain strik- 

 ing differences between the two will be very evident. The first is one of size. 



Greater Diameter of 

 Calice. 



P. sleanm. . . . 

 P. pedroensis. 



18mm. 

 12 mm. 



Lesser Diameter of 

 Calic«. 



12.5 mm. 

 10 mm. 



Height of 

 Corallum. 



12 5 mm. 

 18-f mm. 



The costie and the number of septa are different in the two species, but a 

 much more important difference has not yet been brought out in the discussion. 

 Verrill says of the septa and pali in P. sfenrvsi: "The primary and secondary 

 septa are considerably broader than the others, broadly rounded and somewhat exsert 

 at summit, narrowed toward the base, and divided into tiro or three unequal, broad, 

 stout, paliform teeth, which are rough and lacerately spinulose at summit '" 



' The italics are used by the author of the present paper. 



October 28, 1002. 



