^''is'j:"'] PROCKKhlN'CS Ol' llll-: XA'I'IONAI. MIJSKIJM. 457 



Tlic spiiu', is iKMily straiulit iiiid tapers svmiiictiicall.N to an aciito 

 ;i)i('X. The head is roiiiidfil and looks slij;lill.v inwards, and its siirlacc 

 is slii^Iitiy pnxluccd inwards and backwards in a low IVoc anji^lc. The 

 inner ed^e of the spine is armed with a row of tootli-like processes 

 abont twenty-two in number, widcli are directed backwards. There 

 are no teeth on the external edy;e of the spine. The surface is tlirown 

 into ratlier (!oarse obtuse somewhat irre^uhir h)n[(itudinal riilges, which 

 inoNcuhite more or less, and resemble in jjeneral that of the plate of 

 the shell of the Ilohnicnta nigosd. ICi^htor niiu* rid<,'es may be counted 

 at the middle of the lcn;;tli of the spine. Ijeujjjth of spiiu' HI milli- 

 metres, width at basi! 11 millimetres, at middle 7 millimetres. 



Kroni Mansfield, Pennsylvania, collected by A. C Sherwood Ibr ]{• 

 J). Lacoe. 



V. — On the rAiiiEu fins of Megaliciitiivs nitidus Cote.* 



This species was referred by me to a genus distinct from Megalichthys 

 on account of the auuuhir ossification of the vertebra*, those of the latter 

 iienus luiviui; been described by an I">n<ilish anthority as am])]iic(elons. 

 Dr. Traquair has, however, shown that the vertebra' of the jl/t'//a//(7////(/\ 

 hibhcrlii are annular, and specimens kiiully sent me by Mr. John Ward, 

 of Longtou, Staffordshire, and identitied as belonging to that genus, 

 (pnte, resemble tliose of the M. nifidiis. 1 therefore provisionally, at 

 least, w ithdraw the generic name which I conferred on the latter. It 

 is not uncommon in the Permian bed of Texas. (Fig. ^■) 



1 have described the basis of the posterior part of the skull in this 

 si)ecies and in the smaller .1/. cicrrojiiufi ('ope,t and I can iu)w giv(> an 

 acirount of the characters of the limbs. I am emibled to do this by mak- 

 ing longitudinal sections of both anterior and posteriin' lind)S of both 

 sides of the lint^ specimen of the ^1/. iiitidus, which served as the type of 

 niy original <les(!ription, (Pig. 0.) 



The paired tins or limbs are of the "obtusely lobate" type according 

 to Woodward, but approach those of the Arthrodira very distinctly. 

 The general form is short for a fin of the unibasal type, as it is fusiform, 

 terminating in a rather rapid acumination. The sui)erior, exterior, and 

 inferior faces are CO vere«l with small s(;ales covered with ganoine, and the 

 rays are conlified to the internal edge. The axis of the pectoral tin con 

 sistsof a single robust element, probably cartilaginous, but invested with 

 a thin layer of dense bone. The interior structure is cellular, the cells of 

 irregular anuebiform outlines, and surroumled by a distinct layer col- 

 ored like the matrix, and not like the osseous tissue. This element ex- 

 tends to the extremity of one of the tins which has unfortunately lost 

 its apex. On the other it disappears at three fifths the distance from 

 the base, owing probably to the obliquity of the section. On the in- 



'EvtostcorhacliiN uUidiis Vo\h\ Proceed. AiiuT. Philos. Soc, IH^O, p. .^lO. 

 t lioc. cit.. l-s:?, ]). Ci'id. 



