THE GENUS SYRINGOPLEURA SCHUCHERT 549 



specimens coming before me all belonged to an abundant species, 

 while 6". randalli represents a different and much rarer one. The 

 probabilities appear to me decidedly adverse to this hypothesis, 

 however, and the following statement of Professor Schuchert's 

 is in point. He writes of Syringothyris: "At no time, however, 

 was there more than one species in a fauna, and all these are very 

 much alike." 



Thanks to the courtesy of the Academy of Natural Sciences of 

 Philadelphia, I have been able to examine the type specimens of 

 S. randalli, and this examination seems to bear out the opinion 

 expressed above. The specimens sent me as the types are three 

 in number (Nos. 9532, 9533, and 9534), only one of which, however, 

 was figured in connection with Simpson's description. 1 It is 

 an internal mold of a ventral valve. It is a fact that this speci- 

 men shows some very obscure, longitudinal markings at the bottom 

 of the sinus, but it is also a fact that Simpson's drawing exagger- 

 ates these unpardonably. 



When fossils are preserved as molds, the best opportunity to 

 observe external characters is naturally afforded by molds of the 

 outside. In the case of such species as S. randalli, internal molds 

 of the dorsal valve are more satisfactory than internal molds of 

 the ventral valve, because testaceous deposits on the inner surface 

 of the shell which tend to obscure such external features as the 

 plications were there less extensively developed. In internal molds 

 of either valve the marginal portions afford better evidence than 

 those near the umbo, because the secondary deposits were chiefly 

 formed over the older parts of the shell. On the internal ventral 

 mold which is the type specimen of S. randalli, the lateral costae 

 are well shown except in the cardinal and umbonal areas. In this 

 degree of expression they stop abruptly at the sinus. The anterior 

 part of the sinus, where the costae, if present, would naturally be 

 most conspicuously developed, is nearly, if not quite, smooth. 

 The posterior part is occupied by the large umbonal scars. It is 

 in the intermediate portion, where the test was probably still 

 appreciably thickened, though less so than at the umbo, which was 

 filled by the apical callosity, that the obscure radial markings can 



1 Am. Phil. Soc, Trans., XV, 441, Figs. 1, 2. 



