No. 470] OLD AGE IX BR AC If 10 PO DA 



105 



Example: in ageroiitic iH'dicU" \al\c iA s. (trminiKilii.^. .No. <>(<•, 

 the callosity extends 17 mm. from aprx ot ili.' i.> the 



anterior border, uniting the dental liiniclla" and .-fiidin- oti a 

 median portion forward between the jMoicrior cxtKMnnu^ ot iho 

 diductor muscle impressions. In a matiin' \al\f »»! ir.^ 

 there appear only faint indications of this calloMtx ni ilie apex 

 (Figs. 18 and 19). Hall and (Marke (''.)4a, p. ). nu^iiiion this 

 deposit of calcareous matter in the apex of the vaKr a^ a ficnicnt 

 condition in senile Spirifers. Thev also stat(> that "the tendency 

 to contract the pedicle cavity and deltidiiim ])resent.s its extreme 

 manifestations in the Devonian forms of Stropheodonta, Stropho- 

 ncUa and Leptostrophia where it has become almost and some- 

 times quite obliterated and the entire umbonal area filled with 

 testaceous secretions" (Hall and Clarke, '94a, p. 919). 



(2) By the encroachment of the uml)o of the brachial valve 

 upon the delthyrium of the pedicle valve, so as partially or com- 

 pletely to cover it. This follows from the rotation of the umbos 

 toward each other in senescence as already described (p. 99). 

 When its original opening is thus covered, the pedicle may keep 

 its passage free by resorption into the umbo of the pedicle valve, 

 as already seen (Figs. 1, 11, 17), or may become atrophied and 

 disappear, leaving the shell unattached. 



Examples: in a senile specimen of PlatijsiropJna ///?;.r, No- 

 191 1, M. T. T., the umbos are so closely appress(>d that n.) ptMlu ie 

 opening can be seen (Fig. 10). An approach to tlii> ((.iidition 

 is seen in many senile Spirifers, Rhtjnchofrevia capcu', etc. 



9. Disappraranrr of Spinr,'^, Nodci, rfc— In old age the sur- 

 face tends to become smooth, thus repeating the nepionic .surfac-e 

 character. In all forms this is noted first at tlie angles and later 

 at the anterior portion of the shell. There is ,>light de\t-l()pnicnt 

 of surface ornamentation among the l)ra( hi()p<)(l> l»cMinil the 

 simple plications and median sinus and told. 1 In^ hick is r>pr( i- 



entirely (see also Hyatt, 

 Examples are noted in Pr 



