8 THE VOYAGE OF H.M.S. CHALLENGEE. 



Before describing the various species dredged by the Cliallenger Expedition, it may 

 be as well to mention that tlie Brachiopoda have been divided by Bronn into two great 

 groups termed Apygia and JPleuropygia. Professor King, considering these to be inad- 

 missible on certain grounds, substituted the name Clistenterata for the first group, on 

 account of its including animals that are destitute of an anal aperture ; and the term 

 Tretenterata for the second, as it embraces animals provided with this opening. The 

 former division contains species which have their valves articulated, and belong to the 

 following genera and sub-genera — Terebratula, Terebratulina, Waldheimia, TerebrateUa, 

 Magasella, Laqueus, Megerlia, Kraussina, Bouchardia, Platydia, Argiope, Cistella, 

 Gwynia, Thecidium, RhyncJionella, and Atretia, among the recent forms. The latter 

 division comprises species with unarticulated valves, such as Lingula, Glottidia, Discina, 

 Discinisca, and Crania. Some very important modifications in the animal connected 

 with these divisions, especially in what relates to the muscular system, are fully detailed 

 in the anatomical memoirs to which we have already referred. 



Long experience has shown that the subdivision of the large family Terebratulid^ 

 into diff"erent genera and sub-genera, is not only necessary but fully Avarranted by the im- 

 portant diff"erences assumed by the animal as well as by its skeleton or the calcified support 

 of the labial appendages. It is, therefore, my firm belief that we are justified in maintain- 

 ing Waldheimia as a distinct genus or section from Terebratida, just as much as to 

 maintain TerebrateUa as distinct from Terebratula or Waldheimia. I, consequently, 

 regret not being able to agree with my distinguished friend, Dr G-wyn Jefireys, who 

 seems inclined to unite the two first-named genera under the single name Terebratida, 

 nor can I coincide with his statement (Proc. Zool. Soc, April 1878, p. 398): — "It is 

 notorious that Terebratidina and Waldheimia gradually pass one into another, as well 

 as into the main or typical genus Terebratida." My long study of the group would 

 lead me to a completely difi"erent opinion, for not only are the difl^erences presented 

 between the animals of Terebratula and Waldheimia very great, but the characters of 

 their loops are equally distinct. In Terebratida the loop is very short and simple, as is 

 likewise the case in Terebratidina, while in Waldheimia, as so well shown by Herman 

 Friele and by Mr Jefireys himself, it has to go through a very complicated series of 

 changes in the process of its development prior to attaining its full-grown and final 

 condition, namely, that of a long, simple reflected loop. It also supports the principal 

 branches of the labial appendages throughout their entire length, which is not the 

 case in Terebratula or Terebratulina. There exists also in the dorsal valve of Wald- 

 heimia, a median septum which is not present in Terebratida, and which is a 

 constant help to the Palseontologist, enabling him, without seeing the interior of the 

 shell, or its animal, to distinguish in the fossil condition species that belong to Wald- 

 heimia; a dark median longitudinal line being generally observable through the thickness 

 of the shell, and extending from the umbo to about one-third of its length. This is 



