V, — Revision of the Families of Loop-bearing Beachiopoda. 

 By Charles E. Beecher. (With Plates I and 11.) 



The recent publications of Fischer and QEhlertj ^' ^' ^*'' * combined 

 with previous observations by Friele^^ and Deslongchamps,'' furnish 

 material which suggests a natural grouping of the Terebratuloids. 

 The present knowledge is incomplete in some details, especially as 

 regards the fossil genera, yet enough is available to simplify the 

 arrangement of the leading terebratuloid types, and to show their 

 common relationships. By far the best classifications have been 

 those proposed by DalP in 1870, and by Deslongchamps'^ in 1884. 

 Only in the light of recent discoveries is it possible to offer a new 

 arrangement of the genera. 



The suborder Ancylobrachia, proposed by Gray^- in 1848, includes, 

 with some emendations, all the genera currently knoAvn as Terebrat- 

 uloids. Taking Gray's name for the entire group, since it has 

 priority over Kampylopegmata, Waagen,'® 1883, it is found to com- 

 prise two distinct types of brachial structure, each with a separate 

 genetic history. It is here proposed to recognize these two types 

 as of family importance, according to the interpretation of family 

 characters given by Agassiz.^ 



The TerehratididcE. 



In the first family, the Terebratulidse, the loop is always free and 

 may be long or short. It is developed by the growth of two 

 lamellae, or descending branches, from the points of the crura, unit- 

 ing in the median line. The central portion may be narrow or 

 medially expanded. In some genera, recurved ascending branches 

 are produced by the partial resorption of the broad band or plate 

 forming the connection between the descending branches. The cirri 

 in early stages of the animal are centrifugal, or directed outwards. 

 The growth of the loop in Terehratulma has been illustrated by 

 Morse.'' 



Terehratula {Liothyrina) and Terehratulina may be selected as 

 best representing the Terebratulid^; for Discolia, Agulhasia, and 



* The works referred to by numbers are cited iu full in the list appended. An 

 excellent summary and review of Fischer and CEhlert's papers. *• *•• "^ by Miss Agnes 

 Crane,- has appeared in the January number of Natural Science. 1893. 



