Thomson. — Recent Brachiopoda of New Zealand. 



405 



especially those of New Zealand, Australia, Japan, and western North 

 America. When it is further recognized that within the Magellaninae, and 

 probably also the Dallininae, there are different stocks that have arrived 

 independently at similar loop forms, a knowledge of the growth stages 

 becomes of the highest interest. 



Young Stages of Terebratella rubicunda and Terebratella 



sanguine a. 



Through the kindness of Miss Mestayer and Mr. H. Hamilton I have 

 been able to examine a large number of the young of these species from 

 Chetwode Islands (Cook Strait), Wellington Harbour, and Foveaux Strait. 

 Specific discrimination is possible between these two species down to a 

 length of 3 mm. for the ventral valve ; the young of T. sanguinea is 

 in general broader, and the multicostation has already commenced as 

 a crinkling on the margins at that length. So far as the development 

 of the loop is concerned, these two species agree almost entirely with 

 T. dorsata, the development of which has been described by Fischer and 

 Oehlert.* This is only to be expected, since the New Zealand species 

 belong to Terebratella s. str, of which T. dorsata is the genotype. 



Table indicating Names of Loop Stages in Terebratella and 



Magellania. 



In the so-called Magadiform stage (fig. 5) the descending and ascending 

 portions of the loop are separately attached to the septum, and the ascend- 

 ing portion forms a complete ring. This is the condition of the adult 

 loop in Magadina browni, whereas in Magas pumilus the ascending branches, 

 so far as is known, do not unite to form a ring. Moreover, in the growth 

 of the loop of Terebratella the ascending portion never passes through 

 a stage where the ring is incomplete. It is therefore desirable to re- 

 place the term "Magadiform" by "Magadiniform." Similarly the term 

 " Magaselliform " has not been used in an unequivocal sense. It is 

 restricted by Fischer and Oehlert and Beeeher to the stage, later than 

 Magadiniform, where the descending and ascending portions of the loop 

 have united with one another along the side of the septum (fig. 6). This is 

 the stage attained in the adult loop of Magella carinata, but many species 

 classed under Magasella have not passed the Magadiniform stage. Hence 

 it will conduce to clearness if the term " Magelliform " be used for the later 

 stage, and the term "Magaselliform" be used in a wider sense for both 

 Magadiniform and Magelliform stages- — that is, for shells with a high septum 

 rapidly lessening in height posteriorly, and with descending portions of 



* Loc. cit. 



