432 MOLLUSCA—AMPHINEURA SUB-KINGDOM VI 
Plagioglypta, Pils. and Sharp. Surface with extremely oblique. sinuous, encircling striae 
(D. undulatum, Mist.) Carboniferous to Trias. 
Family 2. Siphonodentaliidae. Simroth. 
Scaphopoda having the foot either expanded distally in a symmetrical disk with 
crenate continuous edge, or stmple and vermiform, without developed lateral processes. 
Shell small and generally smooth, often contracted towards the mouth. Cretaceous to 
Recent. 
Although this family is usually characterised by a small smooth shell, the essential 
difference from the Dentaliidae is in the form of the foot. Typical forms of Cadulus 
appear in the Cretaceous; the remaining 
A B C P senera are Tertiary and Recent. 
€ ? Entalina, Monts. Shell Dentaliwm-lke, 
/ largest at the aperture, thence tapering to 
the apex; strongly ribbed, and angular in 
section near the apex. Miocene to Recent. 
Stiphonodentalium, Sars (Pulsellum, Stol. ; 
Siphonentalis, Sars). Shell an arcuate, 
Fic. 791. shghtly tapering tube, circular in section 
A, Cadulus (Polyschides) denticulatus, Desh. Cal- or nearly so, and smooth externally. Apex 
caire Grossier; Damery, near Epernay. Lb, Cadulus 5 : catego a 
(Dischides) bifisswratus, Desh. Caleaire  Grossier ; rather large, typically slit into lobes, but 
Grignon ae Ta peauns gram Emi For. sometimes simple, Plioeene to Revemt, 
tonian ; Monte Gibbio, near Sassuolo, Italy. Cadulus, Phil. (Gadus, Desh. 3 Gadila, 
Gray ; Helonyx, Stimp.), (Figs. 791, C, D). 
Shell tubular, circular or oval in section, swollen near the middle, or anteriorly, con- 
tracting toward the aperture. Cretaceous to Recent. 
Typical forms with simple anal orifice appear first in the Cretaceous, Dischides, 
Jeffr. (Fig. 791, B), with two lateral slits, and Polyschides, Pils. (Fig. 791, A), with 
several notches appear in the Eocene. All continue to the present. 

Class 3. AMPHINEURA. Ihering.! 
Aquatic, marine, bilaterally symmetrical Mollusks, with the head partially or not 
differentiated , in form worm-like with a ventral groove or none, or oval, flattened, 
with a foot adapted for creeping. Nervous system consisting of an oesophageal ring 
with ganglia and four longitudinal cords, two ventral and two lateral ; no cephalic 
eyes, tentacles, or otocysts. Gills paired or many, posterior or lateral ; mouth anterior, 
usually with a radula ; anus posterior, median. Hxternal surface with a series of 
shelly plates, or stiffened with calcareous spicules. 
1 Literature : 
Ihering, H. v., Vergleichende Anatomie des Nervensystems und Phylogenie der Mollusken, 1877. 
Dail, “W. H., On the Genera of Chitons (Proc. N. $8. Nat. Museum, vol. IV. p. 279), 1881. 
Hubrecht, A. A. W., A Contribution to the Morphology of the Amphineura (Quar. Journ. Microscop. 
Soc., vol. XXII. pp. 212-227), 1882. [Bibliography, pp. 226, 227. |] 
Rochebrune, A, T. de, Monographie des espéces fossiles appartenant 4 la classe des Polyplaxiphores 
(Ann. Sci. Geol., vol. XIV. pp. 1-74), 1883. 
Pruvot, G., Sur Vorganisation de quelques Néoméniéns des Cotes de France (Arch. Zool, Exper. et 
Génér. [2], vol. IX. pp. 699-805, 1891. [Bibliography, pp. 702, 703.] 
Pilsbry, H. A., Monograph of the Polyplacophora. In Tryon and Pilsbry’s Manual of Conchology, 
vols. XIV. and XV., 1892-93. 
