O'COXXELL, REVISIOX OF 2 HE GENUS ZAPHREXTIS 183 



and abruptly, leaviug at the bottom a flattened area about fifteen millimeters 

 in diameter ; fossette commencing just posterior to the center and continuing 

 to the posterior margin, much more prominent on the bottom of the calyx ; the 

 larger lamella' continue to the center, slightly twisted ; from six to eighteen 

 denticulations in the space of five millimeters ; near the margins of the cup 

 they are thin and somewhat obscure, on the sides they are very prominent and 

 spiniform. . . . Although usually placed in the genus Zaphrentis, this form 

 presents the characteristics of the genus Heliophyllum." (17,311,12.) 



To the genera Zaphrentis and Caninia was added a third, Hetero- 

 phrentis, by Billings in 1872, to include the species spatiosa, excellens, 

 prolifica and others which were formerly placed under the genus Zaph- 

 rentis. The type is spatiosa, described as follows : 



"Corallum simple, turbinate. Calice large, with a well-defined septal fos- 

 sette, the bottom either smooth or with a pseudocolumella. Septa below the 

 calice sharp-edged, often with their i^nner edges twisted together; above the 

 floor of the calice they are usually rounded, especially on approaching the 

 margin. There is apparently only a single transverse diaphragm, and this 

 forms the floor of the cup." (12, 236.) 



Lambe comments on this genus in his description of Streptelasma pro- 

 lificum, saying, 



"The writer is inclined to believe that the species Heterophrcnti.s spatiosa, 

 Billings, is founded on short and unusually widely expanding specimens of 

 S. prolificum. The two type specimens are from Rama's Farm, Port Colborne, 

 Ontario. Mr. Billings was doubtful as to the validity of the species and con- 

 cluded the original description with the remark that it is "closely related to 

 Z. prolifica, and may perhaps be united with it when its characters become 

 more fully known." (21,117.) 



Furthermore, Billings states that 



"It is difficult, perhaps impossible, to decide whether this group of forms is 

 specifically distinct from H. excellens. The greatest difference is seen in the 

 surface characters. In H. excellens the folds of growth are in general numer- 

 ous and angular, although some are rounded. In H. prolifica they are in gen- 

 eral few and nearly always rounded. In H. excellens I have only been able 

 to make out the septal striije distinctly in one specimen. At 1 inch from the 

 base there are 5 and at 2yo inches 4, in the width of 3 lines. In H. prolifica 

 there are 8 to 10 at 1 inch, and 6 to 8 at 2vi^ inches." (12,237.) 



Since Billings was not certain of the specific distinction of H. spatiosa 

 and H. excellens and considered them as probably only forms of H. pro- 

 lifica, the description of which follows, this latter form then becomes the 

 type of Heterophrentis. 



