134 Mr. J. Wood-Mason on the Genus Deidamia. 
plate brought to a point posteriorly ; its lateral plates oval, 
almost equal in length to the former, the outer ones not divided 
into two halves by a transverse line. Five pairs of abdominal 
appendages are present in the male ; those of the first segment 
are slender, with a single spirally coiled terminal plate; on 
the succeeding ones two long, narrow, terminal plates are 
always present; on the second, indeed, even a third accessory 
inner plate is added ; the basilar joint is much elongated, but 
gradually diminishes in length backwards. 
This species agrees in the general form of its body with the 
Scyllaridee, from which, however, it is essentially distinguished 
by the different form of its antennee, and by its didactyle legs, as 
well as by its narrow sternum. With the Astacide it has 
nothing in common, beyond the lamellar appendage at the 
base of the outer antenne and the didactyle feet, but is in other 
respects perfectly different in structure from them. ‘The genus 
conforms most nearly to the fossil crayfish (Eryon Cuvierit) 
from the Solenhofen Slates, described by Desmarest, in that 
in this latter also a flattened cephalothorax, antenne, and legs 
of similar structure are found; the hind body, however, is in 
that species much narrower than the cephalothorax, and the 
lamellar appendage at the base of the outer antennee much 
enlarged. It forms with that extinct form a transitional group 
between the Scyllaride (Loricata), on the one hand, and the 
Astacidee on the other. 
Polycheles typhlops, C. Heller, 
Beitriige zur niiheren Kenntniss der Macrouren, Sitzungsb. der 
Akad. der Wiss. 1862, Bd. xlv. p. 392, Taf. i. f. 1-6. 
The cephalothorax of this species measures 10 lines in 
length, in front 5, behind 5:4, and across the middle 6 lines in 
breadth. The lateral margins are tolerably sharp and distinctly 
toothed, especially towards the front, the lateral angles pro- 
jecting, with their points directed forwards and outwards. 
The flat upper surface is divided by a distinct, anteriorly 
concave cervical furrow, into an anterior and posterior moiety, 
the lateral extremities of the same bifurcated outwards into 
two branches running to the margins, and there enclosing a 
triangular lateral area. Along the middle there runs from 
before backwards a sharp toothed ridge; another shorter and 
weaker longitudinal ridge is found on each side on the hinder 
half of the cephalothorax, somewhat nearer to the lateral 
margins than to the middle line. ‘Towards the front on each 
side lie four or five sharp teeth, one behind the other, in a 
slightly curved, inwardly convex line ; in addition, the whole 
