6io NATURAL SCIENCE. ocr.. 



I. — The Atremata, in whicli the pedicle is free, embraces the genera 

 included in Davidson's family groups of the Lingulidae and Obolidae 

 and the Silurian Trimerellidae. 



2. — The Neotremata, which comprises the majority of genera in the 

 Discinidae, Craniidae, and Siphonotretidaj as established by 

 Davidson. 



3. — The Protremata includes the Orthidae, Strophomenidae, 

 Porambonitidae, ProductidaG, and Thecidiidae. 



4. — The Teleotremata contains the Rhynchonellidae, Spiriferidae, 

 and Terebratulidae of that great authority. 



This scheme possesses the merits of natural grouping from a 

 phylogenetic standpoint. Waagen and Beecher concur in regarding 

 Orthis as the lowest and simplest form of the articulated genera. 

 Mr. Beecher believes Kutorgina to be related to Orthisina and Stropho- 

 mena, of which it is the ancestral type. This is the main point of 

 difTerence between Davidson and Beecher, so far as the relations of 

 genera and families are concerned, as the former never included 

 Thecidimn with the Terebratulidae. Mr. Beecher considers this genus 

 as descended from ancestors with a habit of fixation, so far back as 

 the Silurian, and that its affinities are with the Strophomenoids, which 

 have also a single plate deltidium. Thecidium bears, in his opinion, 

 " the same relation to other Brachiopoda that Ostrea bears to Avicula 

 among the Pelycypoda." It may be added that M. Eugene E. 

 Deslongchamps (15) regarded the division between the Rhyncho- 

 nellidae and Spiriferidae as much less absolute than at first apparent. 

 He cites the recent spinose Rhynchondla from Japanese waters 

 [R. Ddderleini, Dav. MS.) as bearing less resemblance to the Acantho- 

 thyrid, or spiny Rhynchonellae of the Jurassic seas, than to the genera 

 Spirigera and Atrypa of the Palaeozoic oceans." The only known 

 examples of this remarkable "survival" are preserved in the Strassburg 

 Museum, and " a good haul " of this species is much to be desired in 

 the interests of science (13). 



Davidson and King showed very clearly the relations of the 

 Trimerellidae with the Lingulidae, while admitting that from the rudi- 

 mentary characters of the hinge and other external features, they 

 might be regarded as related to the Clistenterata (14). They appear, 

 in fact, to be somewhat intermediate in structure between the two 

 orders. Beecher and Clarke consider it not improbable that phylo- 

 genetic development tended in two main channels, one leading through 

 Strophomena, Orthisina, Lepltrna, Chonetes, Productiis, &c., and the other 

 in the direction of RhynchoneUa, Spivifer, Atrypa, Retzia, and 

 Terehratnla (7). 



The promised continuation of Mr, Beecher's researches on this 

 subject will be awaited with interest. The results already published 

 should induce " species-mongers " to pause in the manufacture of 

 specific designations for ill-defined species, often representing different 



