52 HAV. [Vol. II. 



they become longer and narrower. Professor Cope describes 

 all the centra as having on each side two lateral grooves, except 

 the two or three centra near the head, called by him the 

 " cervicals." However, so far as I can determine, the vertebral 

 centra of the abdominal region have only one lateral groove 

 on each side. Close to the head this groove becomes quite 

 insignificant and is placed close to the pit for the neural arch. 



The attachment of the ribs deserves notice. They are not 

 joined directly to the centra but through the medium of dis- 

 tinct pieces of bone, the parapophyses. These are very short, 

 and are sunken in circular pits so deeply that they scarcely 

 rise above the surface of the centrum. Each has a concavity 

 for the reception of the head of a rib. Some specimens in my 

 possession have the parapophysial pits empty. In others the 

 parapophyses are present, but without rib heads. In a few 

 the head of the rib yet remains. 



Distinct parapophyses are found in a number of fishes, as 

 Cristivomer, Alosa. 



It may be here remarked that the vertebral centra of Tarpon 

 are very different from those of Xiphactinus, being very solid, 

 smooth, and wholly devoid of the deep lateral grooves. Most 

 of the neural arches have become coossified with the centra, 

 and appearances indicate that in the young fish there were 

 separate parapophyses, which later coalesced with the centra. 

 The vertebral column has attained a much higher grade of 

 development than that of Xiphactinus. 



The specimen that I have above referred to X. tJiaiimas, I 

 believe to be such ; but lest it prove to be something else I 

 shall here attempt a description and a comparison with other 

 species. It certainly is not X. dioIossus, since that species 

 has the distal extremity of the maxillary upturned like a saber. 

 Moreover, as I have already illustrated (Fig. 2), the condyles 

 are very different from those of undoubted specimens of X. 

 violossns. It cannot be X. inudgei, since this species possesses 

 four subequal teeth in the premaxtllary, while in my specimen 

 there are present only two teeth. Moreover, the vertical 

 extent of the maxillary behind the posterior condyle is too 

 great. The specimen possibly belongs to X. lestrio. Cope 



