AMALTHEUS LYMENSIS. 391 



■which some authors consider to be synonyms of Amal. oxynotus, are certainly very 

 diiferent species according to our reading of their outlines, markings, and lobe-lines. 



Amaltheus Ltmensis, Wright, nov. sp. PI. XLVI, figs. 1 — 3. 



Diagnosis. — Shell discoidal, much compressed ; whorls extremely involute, umbi- 

 licus occluded by the volutions ; outer whorl very high, nearly two thirds the diameter 

 of the shell ; sides regularly convex, covered with delicate sigmoidal folds, which make 

 one sweep without interruption from the inner to the outer margin ; siphonal area thin, 

 sharp, and cutting, aperture lanceolate, nearly half its height occupied by the turn of 

 the penultimate whorl. 



Dimensions. — Transverse diameter 105 millimetres; height of the last whorl 65 

 millimetres ; width 21 millimetres. 



Description. — This beautiful Ammonite is the southern representative of Amal. 

 oxynotus of the midland and northern counties. It is found in a thin bed of dark pyritic 

 marl near Black Venn, between Charmouth and Lyme. This species is highly charged 

 along the septa with sulphide of iron, whilst the chambers are filled with crystaUised 

 carbonate of lime ; these specimens are, therefore, well adapted for cutting and polishing 

 from the beautiful contrast afforded by the ferruginous and calcareous elements of which 

 this fossil is composed. 



The sides are regularly convex, and ornamented with from fifty to sixty sigmoidal 

 folds, which proceed in regular order from the inner to the outer border, the upper curve 

 of the rib being inclined towards the aperture (fig. 1) without any change in the angle of 

 the ciu've or bifurcation in the rib itself, as seen in Amal. oxynotus (fig. 4) ; the outer 

 whorl embraces the entire shell, and the umbilicus is entirely occluded thereby. 



A section of one of the shells, 45 millimetres in diameter, discloses some points in 

 the anatomy of the shell which cannot otherwise be observed in the outer whorl of this 

 specimen. There are twenty-five chambers, each being surrounded by a thin line of 

 sulphide of iron, the septa between the iron lines being composed of carbonate of lime. 

 The whorls in this specimen are six in number and they are all filled in with crystallised 

 carbonate of lime. The shell is extremely thin, consisting of two lamina, on the outer of 

 which fine hair-like lines of growth impart a delicate and ornate sculpture to it. 



The lobe-line is very complicated. I have had a good example carefully figured from 

 an accurate tracing on the mould (fig. 3). The siphonal lobe is wide, and has two 

 small lateral and one large terminal branch on each side, the two sides forming pairs. 

 The siphonal saddle is as large as the lobe, and terminates in two large, bi-lobed folioles, 

 and three smaller, two on the outer and one on the inner side of the saddle. The pnn- 



