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spine on the anterio-lateral margin belongs to the mesobran- 

 chial lobe. 



The metabranchial lobe is very large. About at its middle 

 is a sharply marked, somewhat rounded keel, which runs nearly 

 parallel with the longitudinal axis, as the two keels from 

 their respective sides only converge slightly forwards. This keel, 

 which is very conspicuous in the casts as well as in the spe- 

 cimens with shells, forms 'something like an extension of the 

 elevated part of the mesobranchial lobe , from which it is 

 however separated by a furrow. Frequently a couple of points 

 on the keel, especially in the casts, give indications of little 

 nodes. The part of the lobe situated outside the keel is rather 

 strongly excavated, and the same is the case, in a somewhat 

 less degree, with the part inside the keel. 



The orbits are, as usual in the genus Coeloma, very large 

 and deep ; they reach from the anterio-lateral margin right to 

 the front. Their top border, the supraorbital border, is men- 

 tioned above. Downwards they are bordered by the infra-orbital 

 margin, which from the front spine of the anterior margin 

 curves strongly downwards , and at the same time somewhat 

 forwards, and rather near to the front forms a strong, flat spine 

 which is placed a little lower than the spines of the front, and 

 reaches about as far to the front as the latter ones. Beside 

 this spine is a somewhat smaller, flattened spine or tooth, 

 which forms the end of the infra-orbital margin. This margin 

 also, like the supraorbital margin, is ornamented by a regular 

 row of little nodes. The orbit is indistinctly divided into two 

 parts, separated by the sht between the two infra-orbital teeth; 

 the latter is continued as a very indistinct furrow into the orbit. 

 The inner part of the orbit is much smaller and flatter than 

 the outer part, and served to hold the stalk of the eye, while 

 the outer part held the eye itself. The stalk of the eye is 

 short and rather thick. 



The flanks form towards the front (near the anterior-side- 



