HETEROCARPUS VICARIUS. 149 
of the orbit, on a level with the base of the eye-stalk, runs backward and 
a little downward along about two fifths the length of the carapace, then 
each side of the carapace. The uppermost of these, lettered a in the accompanying cuts, begins at the pos- 
terior boundary of the orbit, just behind the base of the eye-stalk, runs backward defining the lower limit of 
the gastric and cardiac regions, and ends near the hind margin of the carapace just at the point where the 
hind margin curves backward to form the hind margin of the branchiostegite. The middle lateral carina (4) 
a 
a 
b 
ec 
c 
Fie. 1. Fic. 4. 
a__——_} a 
b b 
ce 
Fic. 2. Fic. 5. 
Fie. 3. Fic. 6. 
originates anteriorly in the orbital spine and courses backward over the hepatic and branchial regions, below 
carina a. The lowermost lateral carina (¢) is continuous in front with the lower spine of the antero-lateral 
border (the branchiostegal spine of Stimpson), and sweeps backward below Z along the branchial area until it 
is lost near the hind border of the carapace. This complete expression of all the carine is represented in the 
first diagram (Fig. 1). It is realized in H. carinatus Smith (= H. ensifer, juv.?), in which all the carine are 
developed throughout their whole course, although @ is not so sharply defined on the anterior half of the cara- 
pace as it is posteriorly. Still it can be followed quite up to the margin of the orbit. The next diagram 
(Fig. 2) shows the complete suppression of the anterior half of a. This condition is exemplified in H. ensifer 
A.M. Edw. In the majority of the known species, however, a is perfectly developed, while J is well-nigh 
completely obsolete (Fig. 3). We then have two lateral carine. These are not homologous with the two 
complete carinx of H. exsifer, but with the upper half-carina and the lowest one of that species. A slight ves- 
tige of the anterior end of 4 appears in the form of a short ridge continued backward from the base of the 
orbital spine. In this category come the following species: H. vicarius Fax., gibbosus Bate, orye A. M. 
Edw., dorsalis Bate, alphonsi Bate, hostilis Fax., und afinis Fax. The next stage in the suppression of the 
carine is shown in Fig. 4, where, besides the absence of 4, we note the obsolescence of the posterior fourth 
of c (H. levigatus Bate). In H. alexandri A. M. Kdw., ¢ has completely disappeared, leaving only one lateral 
carina, a (Fig.5). Finally, in H. devis A. M. Edw., all the carine are obsolete (Fig. 6), and we have a 
smooth carapace, as in Pandalus. ; 
The homology of these carine has been misapprehended by some writers. A. Milne Edwards, for in- 
stance, says that the superior lateral carina of H. ensifer is absent in H. oryz, whereas it is in fact the middle 
one that is obsolete in the latter species. 
