64 DR. T. DAVIDSOX ON RECENT BRACHIOPODA. 



formed separation of the lamellae have progressed so far [PL XII. fig. 21], that only a 

 short hand of connection is left betAveen them ; the apertures in the walls have likewise 

 widened, and a narrow slip is all that still combines the lower and the upper parts. 



" The stage of growth illustrated liy [PL XII. figs. 19-21], may properly be designated 

 tlie Megerlea Stage, and it would be difficult to recognize in this state either the 

 individual described in [PL XII. figs. 16 and 17], or the fully developed Waldheimia. 

 In order to become a mature Waldheimia the band between the lamel-processes and 

 the loop must vanish and the connected lamellae must separate." In another figure, which 

 we have not reproduced, " the hinder connection between the wpper and lower parts is 

 completely severed, but the lamelte are still, though slightly, connected." In the nest 

 stage the connection is cut, PL XII. fig. 22, and in fig. 23 we have the most mature Wald- 

 heimia cranium. Here Friele gives figures from one fifth of a line in length up to one 

 line, the smallest of Avhieh is no bigger than a dot. 



Waldheimia cranium has sometimes been confounded with Liothyris vitrea, to which 

 it occasionally bears some general external resemblance ; but the two forms are not only 

 specifically, but completely generically distinct. Mr. Lucas Barrett was able to examine 

 the animal alive, and states that " the oral arms are so fixed to the calcareous skeleton 

 as to be incapable of motion, except at their spiral terminations It has been sup- 

 posed that these conjoined spiral ends can be unrolled like the proboscis of a butterfly ; 

 I never saw any disposition of the kind manifested. This species is more lively than 

 caput-serpentis, moving often on its pedicle, and is more easily alarmed." The cirri are 

 not protruded beyond the margins of tlie valve ; when the shell is closed they are 

 bent up ; no currents were detected by Barrett, though frequently sought for. Dr. Gwyn 

 -leff'reys states likewise {op. cit. vol. v. p. 163) that he has also frequently observed 

 W. cranium turn round its peduncle, apparently in order to improve its position for the 

 purpose of feeding, and that the valves on being touched close with a snap. 



In Van Bemmelen's " Over den Bouw der Schelpen van Brachiopoden en Chi- 

 tonen," 1882, and in his " Untersuchungen fiber den anatomischen und histolugischen 

 Bau der Brachiopoda Testicardinia," 1883, the author enters upon many anatomical and 

 structural details with respect to Waldheimia cranium^ ; he says that the number of caeca 

 on the same part of the shell-structure in very old and young specimens was found to 

 he the same ; this fact, showing that the distance betw^een two caeca (perforations) 

 does not change with age, led him to the conclusion that no i?itussusception 

 occurs diiring the growth of the shell. The bases of the calcareous prisms were found 

 to be very regular-shaped at the margin of the shell (especially in Terehratiila and 

 Terebratulina sept entriona lis) ; they became very irregular towards the older parts. 

 The concentric lines of growth occurring on the outer surface were totally absent on the 

 inner surface, which is explained by supposing the apposition at the margin to stop 

 for some time, while the formation of new layers on the whole under surface continued. 

 In Waldheimia cranium he found the sexes were separate. 



Mr. Albany Hancock describes and figui-es the soft parts of the animal in his admira- 

 ble memoir already so often referred to, and from which I now give a few extracts, with 

 reproductions of his admirable figures of the dorsal and ventral views of Waldheimia 



