456 Our Fresh-Water Planarice. 



long and one broad ; it is linear oblong, and rather narrowish 

 in front, of a pale carnation, bead obtuse, rose colour ; eyes 

 nearly marginal in the rose-coloured part. It has been found 

 in the neighbourhood of Edinburgh, as its specific name im- 

 plies, by Dalyell, Flemming, and Johnston. I have never 

 seen this species. 



The family of Dalyellidce* so called after Sir John Dalyell, 

 who has paid much attention to these creatures, containing six 

 genera, five of which are lacustrine, differs from the foregoing 

 groups, in all its members having the intestine an undivided 

 tube. " They are small animals, of a parenchymatous consis- 

 tency, in which it is often difficult to trace any distinctly defined 

 viscera, or their openings on the surface. The body is ace- 

 phalous, and more or less contractile, with an entire margin. 

 They are either marine or lacustrine; and the latter, in 

 general, lay their eggs enclosed in a cocoon or capsule. Of 

 the mode in which the marine genera are propagated, nothing 

 appears to be known." The fresh- water genera are defined 

 severally as follows : — 



(1.) Dalyellia. Body somewhat compressed vertically, 

 elliptical ; the mouth terminal ; eyes two, parallel, posterior to 

 the mouth and dorsal; ova capsulated. Lacustrine. Dr. 

 Johnston describes two British species, viz. : — Dalyellia helluo, 

 which is narrowed at both ends, most so posteriorly, of a uni- 

 form grass-green colour, with a transparent margin, one to 

 one and a half lines long, inhabiting stagnant waters ; and 

 J), exigua, which in motion resembles a double cone in form, 

 reddish in colour, one-third of a line in length, and an inha- 

 bitant of ponds. The first species has been described by 

 several naturalists ; the second was first noticed by Sir John 

 Dalyell. I am unacquainted with both. 



(2.) Derostoma. Body linear- oblong, rounded at both 

 ends, with two eyes or none ; mouth pitcher-shaped, concealed, 

 opening by a longitudinal fissure on the venter. Two British 

 species are described, viz., D. unvpuncbatvm, which is plump, 

 narrowed towards the anterior extremity, and obtuse behind, 

 dingy yellow, with two yellow eyes, and three lines long, an 

 inhabitant of ponds with a muddy bottom ; and D. vorax, with 

 round body, obtuse in front, tapering backwards to a point, 

 greenish, and without eyes. It is one and a half lines in 

 length, and is found in fresh-water marshes. The generic 

 name, which signifies " long-mouth," from its longitudinal 

 opening, was proposed by G. Duges in 1828. 



* The Planarian worms have been well divided into the two following 

 sections : — 



(1.) Dendeoccels, having a digestive apparatus dendritically branched. 

 (2.) Rhabdoccels, having a straight or unbranched digestive apparatus. 



