M. Lamarck concludes his description of this fossil by saying, that the last chamber is closed by an operculum; a circumstance which M. Picot de la Peyrouse had supposed that he had frequently observed, whilst examining the numerous specimens which he had found on the Pyrenees. The existence of this operculum is however positively denied by M. Denys de Montfort, who considers this supposed operculum as only one of the septa bearing the impression of the posterior part of the animal. Two specimens[1] contain sections of these fossils, towards their superior termination; and shew, perhaps, the inner side of this last septum or supposed operculum; but do not appear to yield any marks which may assist in determining on the real nature and office of these parts.
M. Picot de la Peyrouse, besides finding several of these bodies of a conical form, whose length did not exceed their diameter, found others of a cylindrical form, some of which were a foot and a half in length, though not more than an inch in diameter; and of course nearly as large at one end as at the other. The regular manner in which he found these fossils arranged by the side of each other led him to describe them as resembling the pipes of an organ. M. Denys de Montfort has thought proper to place the fossils of this description under a new and distinct genus, which he names Batolites organisans, (Le batolite tuyau d'Orge.) The hippurite he remarks is constantly bowed and short, and possesses a very thick shell; whilst the batolite on the contrary is straight and long, and has a very thin shell.
In another specimen[2] a section of one of these fossils is seen possessing a much greater degree of curvature than that which is seen in No. 1. which indeed departs but little from the straight line. These two fossils may be regarded as intermediate in their
