324 MAXAC0Z0A. GASTEROPODA. PECTINIBRANCHIATA. 



Shell depressed, rather convex below, considerably convex 

 above, faintly striate, little glossed, obscurely semitransparent : 

 the whorls four, rounded, and very distinctly separated by the 

 suture, the last turn not angulate, nor proportionally larger ; 

 aperture placed obliquely, semilunar, rather wider than long, 

 with the margin thin and direct; the colour umber-brown, 

 deeper beneath, paler toward the apex. Diameter about half 

 a twelfth of an inch, height a fourth less. 



A single specimen found by me, in shell sand, from Ugie- 

 mouth, sent by Mr. Alexander Murray in December, 1842. 

 Being thus in the company of marine shells, one might readily 

 pass it over as a Skenea. Many land and fresh-water Gas- 

 teropoda however occur in the same situation, as at the mouths 

 of our other rivers. The species is easily distinguishable from 

 the other Zonitse ; and specimens presented to me by Mr. 

 Thompson of Belfast and Dr. Fleming, render the identity of 

 my specimen certain. It is perfectly fresh. 



Helix pygmsea. Drap. Moll. Ten. et Fluv. 114. PI. 8. f. 8,9, 10. 

 — Zonites pygmoeus. Gray's Turton, 167. PI. 5. f. 46. — Helix 

 pygmaea. Alder, Mag. Zool. and Bot. ii. 109. 



ORDER II. 

 GASTEROPODA PECTINIBRANCHIATA. P. 50. 



Family III.— Tctrbinina. P. 52, 130. 



Genus 1. Trochus. P. 53, 131. 



Trdchus umbilicatus. Umbilicated Pyramid-Shell. 



Shell umbilicate, depressedly conical, of five sulcato- 

 striate little convex turns, of a reddish-white colour, 

 with radiating, undulated reddish-purple stripes ; the 

 umbilicus rather wide, the apex perforated. TJmbilica- 

 tics, having an umbilicus. 



Shell suborbicular, subdiscoid, or depressedly conical ; with 

 a rather wide umbilicus, pervious to the tip, in which is a 

 small aperture ; the turns five, nearly flat, or little convex, 

 striato-sulcate ; the suture distinct, but very narrow, margined 

 above by a slightly prominent rim ; the last turn angulate, but 

 rounded toward the mouth ; which is very oblique, roundish, 

 and pearly ; the lower surface flattened ; the colour reddish- 

 white, with radiating undulated purplish-red stripes. Diame- 

 ter nine-twelfths of an inch, height five-twelfths. 



An extended examination and comparison haa induced me 



