Notes on the Osteology of the Shad. 225 



XI. — Further Notes on the Osteology of the Shad, (Alosa 

 sapidissima). 



BY FANNY E. M. HITCHCOCK. 

 Bead June 4, 1888. 



In a paper' on the cartilage plates which are developed in the 

 region of the lateral line of shad, I called attention to the evi- 

 dence of the concrescence of the anterior body segments, and 

 the following notes are an outline of some of the results ob- 

 tained while studying the effect of such concrescence on the in- 

 ternal skeleton. 



Beginning with the anterior vertebral elements we find that 

 the epipleurals have disappeared, the ribs and epicentrals of the 

 same segments have coalesced, and passing forward are crowded 

 closely together in the region of the exoccipitals and opis- 

 thotics ; while the epineurals are similarly crowded against the 

 posterior part of the exoccipitals and the supraoccipital, upon 

 the epiotics and the pterotics, and against the parieto-frontal 

 ridge. 



The centra of the corresponding vertebras have either entirely 

 disappeared, or have united with the basioccipital. The lateral 

 walls of the skull, which are formed by the bones of the ear 

 capsules, are very thick, as is also the supraoccipital. 



The parietal bones are wanting, and in place of them is seen 

 on each side of the skull a large foramen which opens directly 

 into the brain cavity. On top of the skull on each side is a 

 deep depression extending laterally into the supraoccipital, 

 epiotic and pterotic bones. The outer lateral and posterior part 

 of the depression deepens, forming a pit which burrows down 

 into the exoccipital bone. In some specimens I could pass a 

 bristle down through this pit into the brain cavity, though in 

 most of the specimens examined there was no connection. 



^ " Preliminary Paper on the Structure of Alosa Sapidissima" (abstract), 

 Proc. Amer. Assoc. Adv. Sci. 1887, p. 259. 



