ASTACID^E. 19 



ov.al, closed by a thick membraneous plate, firmly attached by the out- 

 side half, moving and opening inwardly. The oviduct is a simple hole, 

 and, as far as I know, there are no specific differences. In a new gigan- 

 tic Australian species of Astacoides, very near A. nobilis Dana the female 

 aperture is more elongated and surrounded by a circular barbe of hairs, 

 apparently designed for the better conveyance of the seminal fluid in a 

 species without first abdominal first legs. 



The manner of coition of the Astacidae has been as yet rarely ob- 

 served (Cuvier Regne anim., T. IV. p. 89, says: " L'accouplement 

 s'opere ventre contre ventre ") ; but, on comparing closely the situation 

 of the sexual parts of the male, it is evident that the first abdominal 

 legs partly enter into the oviduct, and certainly no more than with 

 their corneous tips. The length and situation of the parts, and the cir- 

 cumstance that the second pair of legs is apparently firmly fitted in 

 coition to the first legs so as to prevent a farther entrance, seems to 

 prove that perhaps this arrangement only serves to open the mem- 

 braneous plate of the female parts at the right time. In all the species 

 of Cambarus the part of the first abdominal legs of the male, which may 

 and which can only enter into the female aperture, is well marked and 

 separated by a transverse superficial suture. 



It is well known that the females of the Astacidae possess no recepta- 

 culum seminis, and so the introduction of the seminal fluid seems without 

 purpose. But as it is stated by Milne-Edwards that he once discovered 

 spermatophores in the female aperture of Carcinus, which also has no 

 receptaculum seminis, perhaps the same may occur in the Astacidae. 



Annulus Ventralis. — The female sexual aperture offers no specific char- 

 acters, but we find some in the ventral, or rather sternal, plates between 

 the last two pairs of thoracic legs, especially between those of the fourth 

 pair. These differences not being very remarkable in the true Astacus, 

 although they exist, I never find them mentioned by the authors. But 

 the American Cambarus shows well-defined characters, although difficult 

 to describe. 



Between the fourth legs we find a broad trapezoidal plate, more or 

 less excavated and elongated in the different species. The posterior 

 end of this plate is ordinarily dilated and on every side angularly pro- 

 tracted. Its surface is smooth or tuberculated. Behind this plate is a 

 supernumerary corneous organ (repeated even between the fifth legs), 

 which gives specific characters. This organ — named annulus in my 

 descriptions — generally forms a short cone, with a transverse oval base 

 and a depressed tip. This cone is divided in the medial line of the 

 body by a denticulated suture, with inflated margins. The tip is often 

 more or less depressed, or even impressed, forming a deep, transverse 

 hole, crossing the denticulated suture. Tab. II. f. 126. 



We find inside two approximated, inflated, or vermiform ridges, fol- 



