AEGOCERAS LAQUEOLUS. 317 



The siphonal area (PI. XV, figs. 11 and 12) is rounded and smooth ; this is very well 

 shown in the fine drawing of this region in PL XVI, fig. 2 ; but in some specimens there 

 are feeble indications of elevations resembling obsolete ribs, and in others such marks are 

 absent. 



The whorls are almost entirely evolute, the outer simply resting on the penultimate 

 whorl without embracing it (see PI. XV, figs. 1, 2, 10, and PI. XVI, fig. 1). 



The aperture is transversely oblong or subrotund, owing to the greater or less 

 convexity of the sides of the whorls. None of the specimens I have seen enable me to 

 estimate the approximate length of the body-chamber. One of my fragments, however, 

 from Harbury (fig. 2), exhibits well the very sinuous lobe-line this species possesses, and 

 which is now described for the first time. 



The siphonal lobe (PI. XV, fig. 11) is small, with three digitations on each side and a 

 terminal bifid point. The siphonal saddle is large, with four lateral and three terminal 

 festoons ; the principal lateral lobe is large and oblique with two long lateral and a trifidal 

 terminal digitation ; the lateral saddle is as large as the principal lobe, and its sides have 

 six lateral and one small terminal festoon ; the lower lateral lobe is small and oblique, 

 with four lateral and one terminal digit ; the two auxiliary lobes are likewise oblique, the 

 largest has four and the smallest a single festoon, so that the lobe-line of this form is 

 extremely sinuous, as is well shown in the very good enlarged fig. 9, which I have carefully 

 compared with the specimen (fig. 11). 



Affinities and Differences. — This species has been often mistaken for A. Johnstonii, 

 which it very much resembles. It differs from that form in having a wider and broader 

 siphonal area, and is less uniformly round, and less angular than that form ; this is very 

 evident when we compare (PI. XV, figs. 4 and 6) Aeg. intermedium with (figs. 11 and 

 12) Aeg. laqueolus. 



The stronger and thicker ribs, as well as the wider interspace between them, serve to 

 distinguish Aeg. laqueolus, Schlonb., from Aeg. laqueus, Quenst., to which, in other respects, 

 it is nearly related. Probably when a greater number of specimens of A. laqueus, Quenst., 

 are discovered, Aeg. laqueolus, Schlonb., may prove to be only a variety of the older 

 species, which is remarkable for being extremely evolute, with a round aperture, having 

 the ribs small, delicate, and numerous, and the body-chamber occupying an entire 

 whorl in length. 



It resembles Aeg. tortile, d'Orbig. ; the specimen figured in PI. XV, fig. 10, having 

 been sent to me as a representative of that species. It differs, however, in some respects 

 from Aeg. tortile, in having a rounder and much broader siphonal area, more oblique 

 ribs, with a more complex lobe-line than the one traced from Aeg. tortile. 



Locality and Stratigrap/tical Position. — All the specimens I have collected belonged 

 to the zone of Angulatum, and this accords with the observations made, apparently with 

 great care, by Prof. Schlonbach. MM. Collenot and Breon collected Aeg. laqueus near 

 Semur in the Angulatum-zone. 



