Classification of the Crustacea M d icjstraca. 155 



Since the papers of Boas and Hansen were written, the 

 necessity for a rearrangement of the Malacostraca has been 

 rendered still more urgent by Mr. G. M. Thomson's* 

 discovery of Anaspides. This remarkable form presents a 

 combination of characters which indicate for it a very isolated 

 place in our classification. It is not merely a schizopod 

 without a carapace. The double series of epipodial lamellaj, 

 the segmentation of the thoracic limbs, the double gnatho- 

 basic lobes of the first pair, and the apparent distinctness of 

 the first thoracic somite from the head f are among the 

 characters which remove it from close affinity with any 

 of the commonly recognized orders of Malacostraca. 

 Though Aitaspides is not by any means like the hypothetical 

 ancestral malacostracan, its unmistakable resemblance to some 

 of the oldest fossil Malacostraca (Uronectes &c.) shows that 

 at least it is a very ancient type. In the classification given 

 below I have regarded Anaspides and its fossil allies as con- 

 stituting a division of equal rank with the Peracarida and 

 Eucarida. For this I have adopted the name Syncarida, 

 formerly proposed by Packard for the fossil forms alone. 



The details which Mr. Thomson has given of the internal 

 anatomy of Anaspides are very remarkable, and further in- 

 vestigation on this point is much to be desired. Unfortu- 

 nately no specimens have yet reached this country in a state 

 of preservation suitable for anatomical purposes. The mode 

 of development is also quite unknown. 



With regard to the other orders little need be said here. 

 Claus's investigations \ on Nebalia leave no doubt that the 



* " On a Freshwater Schizopod from Tasmania," Trans. Linn. Soc. 

 London, (2) Zool. vi. pp. 285-303, pis. xxiv.-xxvi. (1894). Cf. also Caiman, 

 " On the Genus Anaspides and its Affinities with certain Fossil Crustacea," 

 Trans. Roy. Soc. Edinburgh, xxxviii. (4) pp. 787-802, 2 pis. (1896). 



t I formerly suggested (Trans. Roy. Soc. Edinb. xxxviii. pt. 4, p. 787) 

 that the "cervical groove" of Anaspides, which was described by 

 Thomson as marking off the first thoracic somite from the head, really 

 represented the line of junction of the mandibular with the maxillular 

 somite, on the ground that owing to the forward direction of its lateral 

 portions the lower ends come to lie just behind the mandibles. I am 

 now disposed to doubt the correctness of this view. There appears to 

 be a tendency in tbose Malacostraca which are without a carapace for the 

 lateral plates (pleural or coxal) of the anterior thoracic somites to become 

 displaced forwards at their distal ends as if to protect the mouth-parts : 

 this is well seen in some Arcturidae, for instance. It seems quite likely 

 that this groove in Anaspides has undergone a similar displacement, aud 

 that it really does define the first thoracic somite, which is not distinct iu 

 any other Eumalacostraca. 



t Especially " L'eb. d. Organism us d. Nebali len und d. syst. Stellunw 

 d. Leptostraken," Arb. Zool. Inst. Wien, viii. (1889). 



