164 



a large triangular area, somewhat concave except where inter- 

 rupted by a broad medial longitudinal ridge. 



Surface with concentric stria? and a few ridges of growth ; 

 test thin, conspicuously punctate. 



A portion of the loop has been illustrated by Mr Etheridge, 

 and very little more of the interior of the adult shell than is 

 there shown is known to me, though a great number of speci- 

 mens have been sacrificed. 



In the adult the medial septum is continued to near the 

 front of the valve, and at about half its length it gives off on 

 each side a flatly expanded process by which it is connected 

 with the diverging portions of the loop. The septum does not 

 appear to have been elevated, as in 31. Gamingiana. If the 

 specimen to which the following description refers belongs to 

 31. Wbodsiana, then little remains to complete our knowledge 

 of the interior of the species. Mr. Woods writes : — " Septum 

 round and solid, lamella? of loop widening to the point of 

 attachment, becoming again contracted at the reflection, and 

 then extending into an almost complete circle with a slight 

 projection towards the hinge." 



In young specimens the septum assumes different forms, as 

 I have proved by the examination of more than a dozen speci- 

 mens from the River Murray cliffs and Muddy Creek. In one 

 from near Morgan the septum is actually adherent to the 

 opposite valve, and the loop shows the same disposition as in 

 31. compta (pi. x., fig. 6e). Between this form of septum and 

 that of the adult every possible gradation is exhibited. 



Dimensions.- — Length, "75 ; breadth, "55 ; depth, - 4 of an inch. 



Observations. — 31agasella Woodsiana bears a considerable 

 external resembance to the recent 31. Cumingiana, but differs 

 in its less trapezoidal shape, and in the greater breadth and 

 height of the deltidial area. Internally the characters are 

 widely different in detail, and the thick mesial ridge in the 

 interior of the peduncular valve of 31. Cumingiana is peculiar 

 to that shell. The Port Jackson specimens of Magasella pre- 

 sented by the Rev. Mr. Woods, who directed my attention to 

 the similarity between it and the Mount G-ambier fossil, seems 

 to me to agree better with Reeve's Boucliardia Jibula than with 

 Terebratella Cumingiana, but which Mr. T. Davidson believes to 

 be only a varietal form of the latter. 



Locality and Horizon. — Upper Murravian, near Morgan, and 

 at Muddy Creek (Tate) ; Lower Murravian, at Morrundi, on 

 the River Murray, near Blauchetown ; Mannuin ; and near 

 Callington (Tate). Mount Gambier (Woods & Tate). Yellow 

 calciferous sands, Aldinga Bay ; and at Stansbury (Tate). 



