38 CAR130X11ER0US CEPHALOPODA OF IRELAND. 



(another example) is drawn from the broader a>pect. These figures show the 

 ellipsoidal shape, whether natural or induced, of tlie species. 

 Loraliti/. — Little Island, near Cork. 



BtJSTHENOCiii.'AS,' geu. nov. 



This genus is founded upon two Irish species described by de Koniuck ° under 

 the names Ci/rfoceras HuUi and Ci/rtoceras Bailyi. I shall endeavour to show 

 that tliese species do not belong to the genus to which they were assigned by de 

 Koninck, but that they are intermediate in their structure between Orthoceras 

 and Gi/rtoceras. From the latter they are excluded by the general straightness of 

 the shell, by the nearly central position and apparently cylindrical form of the 

 siph uncle, as well as by the great depth of the chambers in the proximity of the 

 body-chamber in the adult shell. From the former they differ in the sharp, 

 hook-like curs'ature of the shell in the young, and in the peculiar arching of the 

 septa on the dorsal (concave) aspect of the shell. 



These oscillations between Orthoceras and Gijrtoceras seemed to justify the 

 separation of this type from both, rather than to sink its individuality in either, 

 and thus to lose sight of it as a connecting link between them. These connecting 

 forms are as I'are as they are interesting, hence it is the more necessary that they 

 should be strictly characterised. 



In Eusthenoceras, as appears from the enumeration of its structural features 

 above given, there is, on the w'hole, a leaning towards Orthoceran ; the sutural 

 characters, however, differ as already shown in important points from OiiJiucems 

 on the one hand, and from Cijrtoceras on the other. From the former by their 

 arching on the concave curvature of the shell, from the latter by their great width 

 anteriorly. 



A diagnosis of the genus En^thenuceras may be thus constructed : — Shell 

 large, typically curved only in the apical portion ; septa at first approximate, 

 afterwards becoming very widely separated ; sutures arching upwards on the 

 dorsal or inner curvature of the shell ; siphuncle subcentral in the sense of the 

 ventral region, apparently cylindrical. Type, Cyrtoceras HuUi, de Koninck. 



I have included Gijrtoceras Baih/i in this genus, although the single individual 

 representing it departs in some particulars from Eusthenoceras Hidli, — that is, the 

 chambers do not become deeper as they approach the body-chamber, the curva- 



' Itoui £wo-6e>»;s, stout; Kepas, a horn. 



- ' Auuales de la Sot-iete Greologiqiie de Belgiquf,' timi. ix, 18S1-2 (Memoires), pj'. 50 — GO, "Sur 

 quelqiies Cephalopodes nouveaux du calcaire carbonifeve de I'lrlaude." 



