66 THE VOYAGE OF H.M.S. CHALLENGER. 



As rewards 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 ' 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 stiU more so, all the marginal spines, however, being 

 fui-ther 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. 12. 



In Protosquilla trispinosa {Gonodactylus trispinosus, Miers, Squillidas, 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, Squillidaj, 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 fur cicaudata {Gonodactylus furcicaudatus, 

 Miers, Squillidse, pi. iii. fig. 1 4) 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 Une, 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 XVI. fig. 1), the margmal 

 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, Ijut 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 hradyi and Goronida 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. tig. 10. 



