68 University of California Publications in Zoology [Vol. ](3 



striae pass from the depressions between the ridges on the oral shelf 

 aborally on the inner sloping face of the collar for a short distance. 

 The limits of the collar are visible in optical section or inner view only. 

 It is 0.2 oral diameter in height and forms a cone of 30° contracting 

 aborally. 



The bowl is rotund, its length below the collar being 0.88 oral 

 diameter, with only the least trace of external constriction below the 

 level of the inner nuchal ledge. Its diameter is equal to the oral 

 diameter, and its aboral end is almost hemispherical. From near the 

 equator of the bowl there run posteriorly, apparently on its outer 

 surface, parallel, equidistant faint lines. These appear to be shallow 

 depressions and to be almost as many (24 on one face) as the flutings 

 (27) on the oral shelf. Flutings and striae of this sort have not 

 been described in any other species of Petalotricha. 



The wall is composed of an inner and an outer lamella enclosing 

 2-4 layers of alveoli in the nuchal and collar regions and decreasing 

 to one below the nuchal ledge. The greatest thickness at the nuchal 

 ledge is 0.15 oral diameter. Below the ledge it decreases to 0.05. The 

 usual band of circular or elliptical fenestrae, with their long axes 

 vertical, is found on the upper half of the bowl. There are 2-3 irreg- 

 ular rows of areas of unequal size, none over 0.08 oral diameter in 

 greatest diameter, and about 25 across one face. There are indications 

 of a row of horizontally placed fenestrae in the oral rim. 



Dimensions. — Entz, Jr. (1905) does not give measurements for 

 these figures separately. Employing the manufacturer's statement of 

 the magnification of "obj. 6, comp. oc. 4" used by Entz, we arrive at 

 the following: Length, total, lOO/i; collar, IS/n; bowl, 82/i; diameter 

 oral, 87;a ; oral shelf, 98/^ ; nuchal ledge, 62/i ; bowl, 80/i. 



Comparisons. — This species is wholly distinct from the others and 

 is peculiar in the submerging of the oral shelf by the thickened wall 

 of the nuchal region, in the fluted oral shelf and ridged bowl. In its 

 morphological components in the nuchal region and structure of the 

 wall it is, however, clearly a Petalotricha. The thickened wall is sug- 

 gestive of the heavy wall of P. capsa Brandt, and the form of bowl 

 and serrations of some of the varieties of P. ampulla figiired by Brandt 

 (1906), especially var. h. and. in the matter of serrations, vars. d and e. 



Transmitted September SS, 191.5. 



Zoological Laboratory, 



University of California. 



