466 Miscellaneous. 



its back a denticulated cord of pyrites, surrounded by a proper test, 

 which indicates a dorsal cavity of perfectly unusual dimensions. The 

 traces of the septa and lobes stop towards this cord, which is smooth 

 and without septa. At the penultimate whorl, the canal is even seen 

 empty and surrounded by its test ; it may be followed a long way 

 ■with a hair. Below this canal, tbe test of the shell, properly so 

 called, is distinctly seen, and still more internally the siphon. 



M. Quenstedt thus proves that there is a group of Ammonites in 

 which there is above the back a large open canal without septa, 

 separated from the siphon by a wall, which is the true test of the 

 shell. He calls the Ammonites of this group Dorsocavati. 



It remains to determine the function of this canal, which only 

 occurs in a small number of types, otherwise very different from each 

 other. It is not to be supposed, in fact, that all the Ammonites 

 which have a dorsal keel are true A. dorsocavati ; thus the A. Tes- 

 sonanus, D'Orb., presents a perfectly compact fracture. The true 

 Ammonites of this group always present a continuation of the test of 

 the shell at the base of the dorsal canal, so that the keel is detached 

 with facility, and may lead to error. 



]M. Quenstedt indicates some species which should be placed in 

 the group of the Dorsocavati. He has observed the organization 

 above mentioned in A. radians from the lias, converted into lime- 

 stone ; and in the species which he calls Canuliculatus alhus, if 

 it is not detached from the rock, and if in consequence its keel is not 

 fractured. He shows that the A. canaliculati of the white Jura are 

 thus distinguished from those which belong to older strata, for they 

 are dorsocavati, whilst the latter are uot so. In connexion with 

 this he removes some errors of synonymy. — Leonhard and Bronn, 

 Neues Jahrbuch, 1857, p. 544 ; and Bibl. Univ. 1858, Bull. Sci. 

 p. 287. 



Note on the Larvce of the Spiny Lobster (Palinurus). By jNI. Coste. 



M. Coste has lately communicated to the Academy of Sciences in 

 Paris the interesting statement, that the young larvse produced from 

 the ova of Palinurus are identical in structure with the well-known 

 pelagic genus P^y//o5o??m, of which the species have hitherto been found 

 principally in the Indian Seas. These young Crustacea have a flattened, 

 membranous, diaphanous body, divided into two shields ; of these 

 the anterior, which is very large, forms the head ; and the second, 

 which is much smaller, bears the foot-jaws and the five pairs of feet, 

 and terminates posteriorly in a short, slender abdomen. The eyes, 

 as in Pliyllosoma, are borne upon long footstalks ; the feet are com- 

 posed of the same number of joints, terminated by strong claws, and 

 furnished at the second articulation with an appendage composed of 

 three principal pieces, of which the last is furnished with barbs on 

 each side, themselves provided with barbules. In all these points 

 the larvse agree exactlv with Phyllosoma, so that there is some reason 

 to suppose that this genus, like Zuea, will have to be erased from the 

 system..— Cowjj/es Rendus, March 22, 1858, p. 547. 



