310 ESCHARID^. 



with ; and I have seen a space, formed by an aborted cell, 

 occupied by a group of four or five. In some cases the 

 cells are bordered by a raised line; but it is more com- 

 monly wanting. I have never met with more than two 

 spines, and in a large proportion of cases there are none. 

 Smitt, however, states that there are usually four in the 

 younger colonies. 



Habitat. On shells, stones, Ascidians, the tubes of 

 Annelids, &c. from moderate depths. 



Locality. Coast of Northumberland (Alder) . 

 , Geographical Distribution. Finmark, on Rhyncho- 

 nella (Loven) : Spitzbergen (Swedish Exped.) : Green- 

 land (Liitken) : Gulf of St. Lawrence (Dr. Dawson) . 



Range in Time. Postpliocene, Canada (Dawson), 



There is a close relationship between this species and 

 L. adpressa ; but I have no doubt that they are properly 

 accounted distinct. L. hippopus is much the larger of 

 the two, and assumes in the adult state a much more 

 massive character and a coarser habit. The mouth is 

 very similar in both ; yet there are differences which, if 

 slight in themselves, are not without significance in the 

 aggregate. In L. adpressa it is narrower and taller in 

 proportion to its breadth than in the other form, the 

 constriction takes place higher up, and the projections or 

 denticles on the side are less strongly marked. On the 

 other hand, in L. hippopus the upper part of the mouth 

 expands considerably, the lateral projections are promi- 

 nent, and are placed immediately above the lower margin, 

 and the length is less in proportion to the breadth. In 

 the former species avicularia and, I believe, spines are 

 always wanting; in the latter there is no trace of the 

 knobs, which are almost always present in greater or less 

 quantity on L. adpressa, and which are often so striking 



