432 MOLLUSCA AMPHINEURA SUB-KINGDOM vi 







Plagioglyptti, Pils. and Sharp. Surface with extremely oblique, sinuous, encircling striae 

 (D. undidatum, Miinst.) Carboniferous to Trias. 



Family 2. Siphonodentaliidae. Simroth. 



Scaphopoda having the foot either expanded distally in a symmetrical disk with 

 crenate continuous edge, or simple 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 

 D genera are Tertiary and Recent. 



Entalina, Monts. Shell Dentalium-Iike, 

 largest at the aperture, thence tapering to 

 the apex ; strongly ribbed, and angular in 

 section near the apex. Miocene to Recent, 



Siphonodentalium, Sars (Pulsellum, Stol. ; 

 Siphonentalis, Sars). Shell an arcuate, 



791. slightly tapering tube, circular in section 



A, Cadulus (Poiyschiik*) di'nti.niiatiix, Desh. Cai- or nearly so, and smooth externally. Apex 

 caire Grossier ; Damery, near Epernay. B, Cadulus ,, -, n ij. -A i T. 



(inwhitin) htflssunitus, Uesh. Caicaire Grossier; rather large, typically slit into lobes, but 

 Grignon, near Paris c, uuiuius omhnn Phil. Tor- sometimes simple. Pliocene to Recent, 

 toman ; Monte Gibbio. D, Cadulus olii-i, 8cac. Tor- 

 tonian ; Monte Gibbio, near Sassuolo, Italy. Cadulus, Phil. (Gadus, Desll. ; Gad^la, 



Gray; Helonyx, Stinip.), (Figs. 791, G, 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. 1 



tic, 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. External surface with a series of 

 shelly plates, or stiffened with calcareous 



1 Literature : 



Jhering, H. v., Vergleichende Anatomic des Nervensystems und Phylogenie der Mollusken, 1877. 

 Doll, W. H., On the Genera of Chitons (Proc. N. S. Nat. Museum, vol. IV. p. 279), 1881. 

 Hubrecht, A. A. W., A Contribution to the Morphology of the Amphineura (Quar. Jouru. Microscop. 



Soc., vol. XXII. pp. 212-227), 1882. [Bibliography, pp. 226, 227.] 

 Rochebrune, A. T. de, Monographic des especes fossil es appartenant a la classe des Polyplaxiphores 



(Ann. Sci. Geol., vol. XIV. pp. 1-74), 1883. 

 Pruvot, G., Sur 1'organisation de quelques Neomeniens des Cotes de France (Arch. Zool. Exper. et 



Gener. [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. 



