GONIATITES. 



GONIATITES. 



1070 



internal plates (septa) with the inner surface of the shell. lu Ammo- 

 nites this suture is undulated or angularly bent into lobes and sinuses ; 

 in Nautilus, even or gently waved. The exceptions to this are few, 

 but remarkable. Nautilus ziczac of Sowerby (Dr. Buckland's ' Bridge- 

 water Treatise,' pL xliii. fig. 3) has sutures waved as much as some 

 true Goniatites, and there is in fact every degree of sinuosity in the 

 edges of the septa of the nautiloid and ammouitic families. 



M. Von Buch supposes the sinuous edges of the septa of Ammonites 

 to be necessarily derived from the dorsal position of the siphuncle. 

 " All the other differences," says he, " are derived from this capital 

 distinction. The Nautilus, which passes a very large siphon through 

 the middle of the septa, appears sufficiently attached by this mem-' 

 brane to the basis on which it rests. There is no need of any other 

 support, and the septa remain in general smooth and concave without 

 sinuosities on the edges. The small dorsal siphon of the Ammonites 

 would not suffice to secure the animal from displacement on the 

 surface of its cell." Other supports are necessary, and they are found 

 in the marginal lobes which the form of the animal impresses on the 

 partitions of the chambers. These are generally six in number ; one 

 ventral V, one dorsal D, and two on each side L, L'. (See fig. 1 ; and 

 Dr. Buckland's ' Bridgewater Treatise.') 



Fig. 1. 



M. Von Buch, viewing Goniatites as a section of Ammonites, 

 presented the following characters of the group in 1830 : 



The lobes of the septa are completely deprived of lateral denticu- 

 lations or symmetrical crenatures, so that their contour presents 

 always a continuous uninterrupted line. The siphon, compared to 

 that of other Ammonites, is small and delicate ; the strife of growth 

 are gigmoidal on the sides (as in fig. 2), inflexed from the aperture on 

 the back, go as to form a sinus there in the aperture, thus resembling 

 Nautili; whereas in Ammonites generally the striae advance along 

 the dorsal line supported probably by the siphon. The last chamber 

 of Goniatites extends, according to Count Munster, more than one 

 turn beyond the concamerations, but in Ammonites only three-fourths 

 of a turn. 



Later investigations have scarcely modified these fundamental views, 

 except by showing a greater variety in the forms of the sutures than 

 was at first expected. 



Eighteen species of Goniatites are distributed by Von Buch in the 

 following manner : 



Sutures with rounded lobes : 



a. Dorsal lobe simple 4 species. 



b. Dorsal lobe double ... .1 species. 

 Sutures with pointed lobes : 



a. Dorsal lobe simple 6 species. 



b. Dorsal lobe double ... .7 species. 

 Count Munster ('Ann. des Sci. Nat.,' 1834) gives 22 ascertained 



and 4 doubtful species (mostly different from Von Buch's) from the 

 Fichtel-Gebirge. His arrangement is different, namely : 

 1 With simple lobes slightly sinuous and 



rounded ... ... 4 species. 



2. With angular or linguiform lobes : 

 t a. Shell entirely involute, sutures with one 



lateral angular lobe ... .8 species. 



i. Shell entirely involute, sutures with two 



lateral lobes 4 species. 



c. Shell evolute, three lateral lobes . . 6 species. 



Doubtful species * species. 



Martin, in 'Petrificata Derbiensia,' 1809, figured two species of 



Goniatites: Sowerby, in the 'Mineral Couchology of Great Britain,' 

 added two others; and Professor Phillips, in the second volume of 

 the ' Illustrations of the Geology of Yorkshire,' 1836, has raised the 

 number of British species from the carboniferous limestone, mill- 

 stone-grit, and coal-formations, to 33 species, the septa of which are 

 completely ascertained. , 



Beyrich ('De Goniatitis in Montibus Rhenams Occurrentibus, 

 1837) describes 18 species (8 of them supposed to be new), and 

 presents a general classification of all the Continental species sup- 



posed to be distinct, at that time known by the descriptions of 

 Haan, Von Buch, Munster, Goldfuss, &c. The number of species of 

 Goniatites at present known is about 150. 



In external form Goniatites present an almost complete series of 

 gradations from the involute sub'globular figure, common among 

 Nautili, to the discoid spiral shape of the flattest Ammonites. The 

 following figures, from Phillips's 'Geology of Yorkshire,' vol. ii. pi. 19 

 and 20, will illustrate this : 



Fig. 2. 



' Goniatites truncatus. (Phillips.) 

 Fig. 3. 



Goniatites Listfri. (Sowerby.) 

 Fig. 4. Fig. 5. 



Goniatites ipirorb'u. (Phillips.) 



Goiiiatita Gilsoni. (Phillips.) 



Most of the Goniatites have rounded backs ; a few are cariuated, as 

 G. vittiger and G. rotiformis, Phillips. 



In nearly all the Goniatites the surface is marked by transverse 

 sigmoidally-bent lines of growth ; a few have merely annular strife ; 

 in some these stria? rise into tubercles on the inner edge of the whorls 

 (G. Listen, Sow. ; G. subnodosus, Munst.). The striae are occasionally 

 reticulated by spiral lines. Radiating undulations occur on some of 

 the flatter species ; in a few (G. Gibsoni) there are ribs divided after 

 the manner of many Ammonites ; and G. binodosus, Munster, has 

 two rows of tubercles. In all these particulars the parallelism of the 

 series of Goniatites to that of common Ammonites is very remarkable. 



This analogy with the usual forms of Ammonites is augmented by 

 the occurrence of constrictions on the cast of the interior of the 

 shells. (Fig. 3, c.) These constrictions, corresponding to internal 

 thickenings of the shell, are most remarkable in the involute Gonia- 

 tites. (See Phillips's 'Geology of Yorkshire,' vol. ii. pi. six. fig. 1, 2, 

 24, 26; pi. xx. fig. 1 ; Muuster, in 'Ann. dus Sci. Nat.,' pi. v. fig. 2; 

 and Beyrich, in his ' Dessertation,' tab. ii. fig. 8.) They are parallel 

 or nearly so to the lines of growth, and cross the sutures without any 

 definite relation. They may be viewed as periodical thickenings of 

 the edge of the aperture, and as contributing to strengthen the last 

 chamber of the enlarging shell. They vary as to number and position 

 in individuals of the same species. The aperture of many Goniatites 

 resembles that of the recent Nautilus Pompilius. 



The sutures of the Gouiatites are extretm-ly various, beautiful, aud 

 characteristic of the speuies. Individuals of several of the species 

 have been compared almost from the nucleus to full growth without 

 any great change being visible in the form of the septum (as for 

 instance, G. Listen), but in others this is not the case. The following 

 arrangement and accompanying figures will show the principal 



