78 



interesting little form under notice the mesial septum forms a narrow 

 elevated plate, extending as far and further than the greatest length 

 of the lamellae, which last are fixed to the middle portion of the sep- 

 tum. The remarkable deviation from the general details of the 

 arrangements in this Terehratella has prompted me to examine with 

 care a multitude of specimens of different species belonging to the 

 genus, and I was not a little surprised to find that some few other 

 forms presented a similar arrangement, such as Ter. crenulata, 

 Ter. Cumingii, &c., thus forming a passage into Magas, which last, 

 although generically distinct, can no longer constitute a separate 

 family from the TerebratulidcB. 



4. Terebratella? Cumingii, Dav. 1852, (PI. XlV.fig. 10, 16.) 



Diagnosis. — Shell very thick, ovato-oblong ; larger valve most con- 

 vex, slightly keeled ; imperforated one rather depressed ; beak pro- 

 duced, tapering, not much recurved, and truncated by a small oval 

 foramen, beginning at the summit of the beak, and directing itself on 

 the opposite side to the area ; no visible deltidium ; a concave trian- 

 gular area ; surface smooth, strongly marked by concentric lines of 

 growth ; colour white, or slightly tinged with red ; shell articulating 

 by means of two strong teeth in the larger and corresponding 

 sockets in the smaller valve ; apophysary system very complicated, 

 composed of a mesial longitudinal elevated ti-iangular septum extend- 

 ing to about two-thirds of the length of the smaller valve, and which 

 arising from under the cardinal process and crural base, by a gentle 

 curve reaches and touches the larger valve near to its anterior portion, 

 from whence it descends by an almost perpendicular line to the bottom 

 of the valve ; the calcareous riband-shaped lamellae first proceed from 

 the socket walls, directing themselves by a gentle curve to the ante- 

 rior portion of the septum, to which they become attached before 

 bending on themselves to form a loop ; the arms are of a brilliant 

 red colour. Length 5, width 4, depth 2\ lines. 



Hab. New Zealand. Coll. Cuming. 



Obs. — Two specimens of this remarkable shell have been obtained 

 by Mr. Cuming, and it is one of the most interesting among the re- 

 cent forms, presenting great difficulties from an assemblage of cha- 

 racters peculiar to more than one of the proposed sections. In out- 

 ward shape, character of its foramen, and interior of perforated valve, 

 it much resembles Boiichardia rosea ; its foramen is likewise very 

 similar in position to that presented by several species of Trigonose- 

 miis ; the shape and position of its central elevated septum, which 

 touches a portion of the centre of the larger valve, relates it to Magas, 

 and the disposition of the lamellae to Terebratella. I therefore do 

 not feel certain in what genus this curious shell should be placed : it 

 is not a true Terebratella, but there I have placed it for the present, 

 on account of the form of the loop. 



5. Terebratella Spitzbergensis, Dav. 1852. 



Diagnosis. — Shell ovate, slightly pentagonal, longer than wide ; 

 valves almost equally convex ; beak produced, recurved, and truncated 



