372 Mr. J. W. Davis on a 



any one group must always fall far short of the possible 

 number ; and for this reason it is out of the question for 

 us to attempt the solution of the problem of derivation, or to 

 hope for any solution beyond one within the most indefinite 

 limits of correctness. If, when we take one of the most 

 limited of the groups of the animal kingdom, we find our- 

 selves engaged in a hopeless task, what must be the prospect 

 should we attack the problem of other classes or groups of 

 the animal kingdom, where the species run into the thousands, 

 while they number only tens in the case we have attempted 

 to follow out? Shall we say " ignorabimus " or "impavidi 

 progrediamus," and valiantly chase a phantom we can never 

 hope to seize i 



XLIV. — On a new Species of Gyracanthus, a Fossil Fish 

 from the Coal-measures. By James W. Davis, F.G.S. 

 &c. 



Gyracanthus denticulatus, Davis (sp. n.). 



Spine : length 8*5 inches, greatest diameter (one third the 

 length from the basal extremity) '7 of an inch. The spine is 

 slightly curved, rather more so on the posterior than the 

 anterior surface. The basal portion contracts slightly and 

 has a rounded termination. The exposed part tapers gradu- 

 ally to a fine point. The spine is much compressed laterally ; 

 the anterior portion is rounded ; and a deep cavity extends 

 posteriorly from the base more than one third its length, and 

 is continued internally to within a short distance from the 

 point. The line dividing the exposed part of the spine from 

 that which was enclosed in the body of the fish is very ob- 

 lique ; beginning *7 of an inch from the base in front, it ex- 

 tends across to the back, where it is 3 inches from the base. 

 The basal portion has the usual fibrous character. The ex- 

 posed surface is covered with the ridges and grooves charac- 

 teristic of the genus Gyracanthus ; they extend very obliquely 

 from the posterior to the anterior surface, where they meet 

 with the ridges from the opposite side at a sharp angle ; they 

 are continuous ; but the surface of the ridge is produced at 

 short intervals, so as to present a beaded or tuberculate ap- 

 pearance, especially towards the anterior surface. Extending 

 from the point along the posterior portion of each side is a 

 space which is free from the gyrating ridges and grooves. 

 It is about 24 inches long and '15 of an inch wide ; with the 

 exception of two or three minute ridges running parallel with 



