6o8 NATURAL SCIENCE. o„.. 



the widest distribution. The varieties vcrneuilianus, Lni., and aciitilobattis 

 (Ringueberg) are acmic or indirect divergents originating from the 

 " nealogic " period of O. biloba. The variety varicns is the senile, a 

 paracmic condition derived from the "epheboHc " or mature state of 

 that species. In fact, the ontogeny of this very variable species, 

 which begins Hfe and ends it as a normal orthid, indicates its position 

 as an aberrant species of that genus, and as its abnormality — the 

 bilobed condition — was clearly defined in the specific name, we 

 scarcely see the necessity for removing it from the genus Orthis, 

 as defined by Dalman and established by Davidson, who declined to 

 recognise the bilobate species and its varieties otherwise than as a 

 genuine species of the genus Orihis. There seems even less necessity 

 to disguise so well-known and much-studied a brachiopod as the living 

 Thecidium viediterranenm, Risso, under the sub-getieric designation of 

 Lacazella. If biologists and palaeontologists continue to indulge their 

 Adamite denominative propensities in this direction, the student of 

 the future will lose much time in re-establishing the identity of text- 

 book genera and species. 



Important conclusions are derived from comparisons of the 

 geratologous phases of brachiopodal development when ornamental 

 and other indications of maturity disappear in inverse order to their 

 introduction. Age is expressed in the thickening of the shell, which 

 takes place after the individual has reached adult size, and produces a 

 varicose aspect, or truncated margins, and plications gradually vanish. 

 There is an increase in the vertical diameter, the beak becomes invo- 

 luted, and the deltidium, or deltidial plates, may be re-absorbed. The 

 revolutions of the spirals become thicker and more numerous in the 

 spire bearers. In the senile condition, or final nostologic phase of life, 

 brachiopods, like human beings, shed their ornamental appendages 

 and revert in extreme old age to the characteristics of their "nepionic" 

 or youthful period. Such incidents (like premature baldness) may- 

 even be accelerated and transmitted. If we comprehend Mr. Beecher's 

 argument correctly, the genera and species developed by the processes 

 of " accelerated geratologous heredity," such as Stwphalosia and Austo- 

 leges among the Productidae, generally occur in families after the 

 maximum of genera and species is attained. He c\ies Gwynia, Platydiay 

 Cistella and Kraussina among the recent Terebratuloids and A tretia among 

 the Rhynchonellidse as examples of such nostologic types (9). This 

 view clears up many difficulties. The relative afiinities of Gwyma a.nd 

 Platydia were left undetermined in Davidson's " Monograph, of the 

 Recent Brachiopoda " (12). By some authors Gzvynia and Atretia are 

 regarded as immature forms of other genera. But the swollen appear- 

 ance of the margins of the shell is very apparent in the Australian 

 species [Atyetia hrazieri, Dav.) (6), and indicates maturity. Mr. Friele 

 deduced a similar conclusion as to its generic value from distributional 

 data, as it was dredged in northern waters in great abundance w^here 

 no specimens of Rhynchonella were ever obtained. 



