66 
THE VOYAGE OF H.M.S. CHALLENGER. 
As regards one of the most remarkable peculiarities of the genus, the pushing 
backwards of the marginal spines of the telson, the various species present a most 
interesting series of steps in the process of modification. In Protosquilla folinii 1 the 
outline of the telson closely approximates the prevalent type among the Stomatopoda. 
There are six marginal spines, and the submedians, which project furthest backwards, 
are separated by a well-marked median notch, while the second pair are a little more 
anterior, and the third pair still more so, all the marginal spines, however, being 
further back than they are in ordinary Stomatopods. In the very closely related species, 
Protosquilla elongata, PI. XV. fig. 2, all the spines are fused into a pair of rounded lobes 
on the sides of the median notch, and no traces of the separate spines are visible in a 
dorsal view, although their rounded ends project slightly below the general surface of the 
ventral side of the telson, as shown in fig. 1 2. 
In Protosquilla trispinosa ( Gonodactylus trispinosus, Miers, Squill idee, pi. iii. fig. 10) 
the median notch is faintly indicated, and all the spines are on the convexly rounded 
posterior border of the telson. In Protosquilla cerebralis (PI. XVI. fig. 2) the telson is 
transversely truncated behind, and the spines are all on its posterior edge. In Protosquilla 
excavata (Gonodactylus excavatus, Miers, Squillidae, pi. iii. fig. 12) the spines are obscurely 
indicated, but the lateral ones are now the longest, and the edge of the telson is deeply 
excavated between them, while in Protosquilla furcicaudata (Gonodactylus furcicaudatus, 
Miers, Squillidae, pi. iii. fig. 14) this excavation is carried so far that the median portion 
of the telson has disappeared, and the two marginal spines have approached each other on the 
middle line, evidently as the result of an infolding of the median portion of the posterior 
edge of the telson of the larva. In Protosquilla guerinii (PL XYI. fig. 1), the marginal 
spines have undergone a very remarkable modification in a somewhat divergent direc- 
tion. They are on the posterior edge, and the laterals project as far backwards as the 
submedians, but they have become greatly divided, forming a complicated pectinated 
structure. ' 
As regards the telson, Protosquilla folinii is at one end of a series at the other end 
of which is Protosquilla furcicaudata, but it is difficult to decide which of these forms 
is the one in which the process of modification began. As the telson is long, with a 
convex border, in most Malacostraca, and in the Stomatopod larva, it is probable that 
Protosquilla folinii is the primitive form, and Protosquilla furcicaudata a highly 
modified form, and that the relationship to the other Stomatopoda is through Proto- 
squilla folinii, which must therefore be regarded as one of the closest living allies of 
the ancestral type of the order. 
Outside the genus Protosquilla ; the two species for which I have proposed to establish 
the genus Coronida, Coronida bradyi and Coronida trachura, are very similar to 
Protosquilla, as are also, but in a less degree, the true Gonodactyli. On account of the 
1 Gonodactylus folinii, A Milne-Edwards, Nouv. Arch. Mus. Hist. Nat., t. iv., pi. xviii. fig. 10. 
